CN111965659A - Distance measuring system, method and computer readable storage medium - Google Patents
Distance measuring system, method and computer readable storage medium Download PDFInfo
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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
Abstract
The application is applicable to the technical field of flight time, and provides a distance measuring system, a distance measuring method and a computer readable storage medium, wherein a pulse beam is emitted to a target through an emitter; enabling the collector to comprise at least one pixel block and at least two diaphragms, wherein each pixel block comprises at least two sub-pixel blocks which are sequentially arranged according to the increasing or decreasing order of the size, the size of each sub-pixel block is in positive correlation with the measurement distance and is in negative correlation with the aperture of the corresponding diaphragm, each diaphragm shapes pulse beams reflected by a target in the distance measurement range of the corresponding sub-pixel block, and each sub-pixel block collects photons in the pulse beams shaped by the corresponding diaphragm and outputs photon signals; by enabling the control and processing circuit to calculate the flight time of the pulse light beam according to the photon signals, the distance between different targets positioned at least two measuring distances and the distance measuring system can be accurately measured, and the measuring error is effectively reduced.
Description
Technical Field
The present application relates to Time of flight (TOF) technologies, and in particular, to a distance measuring system, method and computer-readable storage medium.
Background
The distance of the target may be measured using a time-of-flight technique, and a depth image containing depth values of the target may be further acquired based on the distance of the target. Distance measurement systems based on time-of-flight technology have been widely used in the fields of consumer electronics, unmanned driving, virtual reality, augmented reality, and the like. A distance measuring system based on a time-of-flight technique generally includes an emitter and a collector, a pulse beam is irradiated to a target by the emitter and a pulse beam reflected by the target is received by the collector, and a distance between the target and the distance measuring system is calculated by calculating a time from when the pulse beam is emitted to when the pulse beam is received. The distance measuring system can be divided into a coaxial system and an off-axis system according to different arrangement modes of the emitter and the collector. For a coaxial system, a pulse beam emitted by an emitter is reflected by a target and then is acquired by a corresponding pixel in an acquisition device, and the distance of the target does not influence the accuracy of a measurement result; for the off-axis system, due to the existence of parallax, the positions of the pulse beams reflected by the long-distance and short-distance targets on the collector can be changed, so that the measurement result has errors.
Disclosure of Invention
In view of the above, embodiments of the present disclosure provide a distance measurement system, a distance measurement method, and a computer-readable storage medium to solve the problem that the accuracy of the measurement result of the conventional off-axis distance measurement system is affected by the distance between the target and the object and causes an error.
A first aspect of an embodiment of the present application provides a distance measurement system, including:
a transmitter for transmitting a pulsed light beam to a target;
the collector comprises at least one pixel block and at least two diaphragms, each pixel block comprises at least two sub-pixel blocks which are sequentially arranged according to the ascending or descending order of the size, one sub-pixel block corresponds to one diaphragm, the size and the measuring distance of each sub-pixel block are positively correlated and negatively correlated with the aperture of the corresponding diaphragm, each diaphragm is used for shaping pulse beams reflected by a target in the range-measuring range of the corresponding sub-pixel block, and each sub-pixel block is used for collecting photons in the pulse beams shaped by the corresponding diaphragm and outputting photon signals;
and the control and processing circuit is respectively connected with the emitter and the collector and is used for calculating the flight time of the pulse light beam according to the photon signal.
In one embodiment, the collector further includes at least one attenuation sheet, each attenuation sheet corresponds to a sub-pixel block whose measurement distance is smaller than a distance threshold, and each attenuation sheet is used for attenuating the light intensity of the pulse light beam incident to its corresponding sub-pixel.
In one embodiment, the collector further includes an imaging lens, configured to perform imaging focusing on the pulse beam reflected by the target before the pulse beam reflected by the target enters the diaphragm.
In one embodiment, the collector further includes at least two first focusing lenses, each first focusing lens corresponds to one sub-pixel block, and each first focusing lens is configured to focus the pulse beam shaped by the diaphragm to its corresponding sub-pixel block.
In one embodiment, the collector further comprises a filtering unit for filtering out the background light and the stray light incident to the at least one pixel block.
In one embodiment, the aperture distance between two diaphragms corresponding to any two adjacent sub-pixel blocks in each pixel block is equal to the parallax corresponding to the lower limit value of the ranging range of the distance measurement system.
In one embodiment, the control and processing circuit comprises TDC circuits equal in number to all the sub-pixel blocks, each TDC circuit being connected to one of the sub-pixel blocks, the time width of each TDC circuit being positively correlated with the measured distance of its connected sub-pixel block, the time resolution of each TDC circuit being negatively correlated with the measured distance of its connected sub-pixel block.
In one embodiment, the emitter includes at least two light source columns sequentially shifted by a first distance in a preset direction, each light source column includes at least two light sources sequentially arranged in the preset direction, and a distance between two adjacent light sources in each light source column in the preset direction is greater than or equal to a second distance;
the collector comprises at least two pixel columns which are sequentially shifted by a first distance in a preset direction, each pixel column comprises at least two pixel blocks which are sequentially arranged in the preset direction, and the distance between two adjacent pixel blocks in each pixel column in the preset direction is greater than or equal to a second distance;
the preset direction is a vertical direction when the distance measuring system is placed on a horizontal plane, the first distance is larger than or equal to the diameter of the light source, and the second distance is larger than or equal to the product of the total number of light source columns included by the emitter and the first distance.
A second aspect of an embodiment of the present application provides a distance measurement method, including:
controlling the transmitter to transmit a pulse beam to the target;
controlling each sub-pixel block of an acquisition device to acquire photons in the pulse light beams shaped by the corresponding diaphragm of the acquisition device and output photon signals, wherein the acquisition device comprises at least one pixel block and at least two diaphragms, each pixel block comprises at least two sub-pixel blocks which are sequentially arranged according to the increasing or decreasing order of the size, one sub-pixel block corresponds to one diaphragm, the size and the measurement distance of each sub-pixel block are positively correlated and negatively correlated with the aperture of the corresponding diaphragm, and each diaphragm is used for shaping the pulse light beams reflected by the target in the range-measuring range of the corresponding sub-pixel block;
calculating the time of flight of the pulsed light beam from the photon signal.
A third aspect of embodiments of the present application provides a computer-readable storage medium, which stores a computer program that, when executed by a processor, implements the steps of the distance measurement method according to the second aspect of embodiments of the present application.
In the distance measuring system provided by the first aspect of the embodiment of the present application, a pulse beam is emitted to a target by an emitter; the collector comprises at least one pixel block and at least two diaphragms, each pixel block comprises at least two sub-pixel blocks which are sequentially arranged according to the increasing or decreasing order of the size, one sub-pixel block corresponds to one diaphragm, the size and the measuring distance of each sub-pixel block are positively correlated and negatively correlated with the aperture of the corresponding diaphragm, each diaphragm is used for shaping pulse beams reflected by a target in the range-measuring range of the corresponding sub-pixel block, and each sub-pixel block is used for collecting photons in the pulse beams shaped by the corresponding diaphragm and outputting photon signals; by connecting the control and processing circuit with the emitter and the collector respectively and calculating the flight time of the pulse light beam according to the photon signals, the accurate measurement of the distances between different targets positioned at least two measuring distances and the distance measuring system can be realized, and the measuring error is effectively reduced.
It is understood that, the beneficial effects of the second and third aspects may be referred to the relevant description of the first aspect, and are not described herein again.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
Fig. 1 is a schematic view of a first structure of a distance measurement system according to an embodiment of the present disclosure;
FIG. 2 is a schematic diagram of a first structure of a pixel block provided in an embodiment of the present application;
fig. 3 is a schematic structural diagram of a collector provided in an embodiment of the present application;
FIG. 4 is a schematic diagram of a control and processing circuit provided in an embodiment of the present application;
fig. 5 is a schematic diagram of a second structure of a pixel block provided in an embodiment of the present application;
FIG. 6 is a schematic diagram of a third structure of a pixel block provided in an embodiment of the present application;
fig. 7 is a schematic structural diagram of a second distance measurement system according to an embodiment of the present application.
Detailed Description
In the following description, for purposes of explanation and not limitation, specific details are set forth, such as particular system structures, techniques, etc. in order to provide a thorough understanding of the embodiments of the present application. It will be apparent, however, to one skilled in the art that the present application may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present application with unnecessary detail.
It will be understood that the terms "comprises" and/or "comprising," when used in this specification and the appended claims, specify the presence of stated features, integers, steps, operations, elements, and/or arrays, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, arrays, and/or groups thereof.
Furthermore, in the description of the present application and the appended claims, the terms "first," "second," "third," and the like are used for distinguishing between descriptions and not necessarily for describing or implying relative importance.
Reference throughout this specification to "one embodiment" or "some embodiments," or the like, means that a particular feature, structure, or characteristic described in connection with the embodiment is included in one or more embodiments of the present application. Thus, appearances of the phrase "in one embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but rather "one or more, but not all embodiments" unless specifically stated otherwise. The term "include" and variations thereof mean "including but not limited to", unless expressly specified otherwise.
As shown in fig. 1, an embodiment of the present application provides a distance measurement system 100, including:
a transmitter 1 for transmitting a pulsed light beam 300 to a target 200;
the collector 2 comprises at least one pixel block and at least two diaphragms, each pixel block comprises at least two sub-pixel blocks which are sequentially arranged according to the ascending or descending order of the size, one sub-pixel block corresponds to one diaphragm, the size and the measuring distance of each sub-pixel block are positively correlated and negatively correlated with the aperture of the corresponding diaphragm, each diaphragm is used for shaping the pulse light beam 400 reflected by the target 200 in the ranging range of the corresponding sub-pixel block, and each sub-pixel block is used for collecting photons in the pulse light beam 400 shaped by the corresponding diaphragm and outputting a photon signal;
and the control and processing circuit 3 is respectively connected with the emitter 1 and the collector 2, and the control and processing circuit 3 is used for calculating the flight time of the pulse light beam according to the photon signal.
As shown in fig. 2, a schematic diagram of a structure of a pixel block 20 is exemplarily shown; the pixel block 21 includes a first sub-pixel block 211, a second sub-pixel block 212, and …, and an mth sub-pixel block 21m, which are sequentially arranged in an increasing order of size, where m is an integer greater than or equal to 2.
As shown in fig. 3, a schematic structural diagram of a collector is exemplarily shown; the pixel block 20 includes a first sub-pixel block 211 and a second sub-pixel block 212, the first sub-pixel block 211 corresponds to the first diaphragm 241, the second sub-pixel block 212 corresponds to the second diaphragm 242, the size of the first sub-pixel block 211 is smaller than that of the second sub-pixel block 212, and the aperture of the first diaphragm 241 is larger than that of the second diaphragm 242.
In application, distance measurement systems can be divided into coaxial systems and off-axis systems according to different arrangement modes between the transmitter and the collector. For a coaxial system, a light beam emitted by the emitter is reflected by a target and then is collected by a corresponding pixel in the collector, and the distance between the target and the distance measurement system does not influence the position of the pulse light beam reflected by the target on the collector. For an off-axis system, due to the existence of parallax, positions of pulse beams reflected by targets located at different distances on a collector are different, the size of a light spot of the pulse beam reflected by a short-distance target on the collector is larger than that of a light spot of the pulse beam reflected by a long-distance target on the collector, and the light spot offset caused by the influence of the parallax of the system on the pulse beam reflected by the short-distance target is larger.
The distance measuring system provided by the embodiment of the application is an off-axis system, at least two diaphragms with different apertures and at least two sub-pixel blocks with different measuring distances are arranged, each diaphragm corresponds to one sub-pixel block, the measuring distance and the size of each sub-pixel block are positively correlated and negatively correlated with the aperture of the corresponding diaphragm, pulse beams reflected by a target located in a distance measuring range of the corresponding sub-pixel block are shaped through each diaphragm, each sub-pixel block collects photons in the pulse beams shaped by the corresponding diaphragm and outputs photon signals, and when the target is located at a position close to or far away in an acquisition field of view of an acquisition device, the distance measuring system can accurately measure the distance between the target and the distance measuring system, and measuring errors are effectively reduced; the aperture of the diaphragm corresponding to the sub-pixel block with the smaller measuring distance is larger than the aperture of the diaphragm corresponding to the sub-pixel block with the larger measuring distance, and the size of the sub-pixel block with the smaller measuring distance is smaller than that of the sub-pixel block with the larger measuring distance. Because the light spot offset of the pulse light beam reflected by the short-distance target is large, the pulse light beam reflected by the short-distance target is made to enter the sub-pixel block with a small size through the diaphragm with a large aperture, so that the light spot size can be reduced, and a large parallax range can be covered.
In application, the size of the sub-pixel block is positively correlated with the number of pixels contained in the sub-pixel block, that is, the larger the size of the sub-pixel block is, the more pixels are contained in the sub-pixel block. When the collector comprises at least two pixel blocks, the structure of each pixel block is the same, the size of each sub-pixel block is positively correlated with the measurement distance, namely the measurement distance of each sub-pixel block is larger when the size of each sub-pixel block is larger. The number, size and measuring distance of the sub-pixel blocks in each pixel block can be set according to the ranging range of the distance measuring system, and the more the number of the sub-pixel blocks is, the higher the measuring precision of the distance measuring system is.
In application, the ranging range comprises an upper limit value and a lower limit value, the measuring distance can be the upper limit value, the lower limit value or the average value of the upper limit value and the lower limit value of the ranging range, and when the sub-pixel blocks in the pixel block are sequentially arranged according to the ascending order of the size, the lower limit value of the ranging range of the previous sub-pixel block is equal to the upper limit value of the ranging range of the next sub-pixel block; when the sub-pixel blocks in the pixel block are sequentially arranged in order of decreasing size, the upper limit value of the ranging range of the preceding sub-pixel block is equal to the lower limit value of the ranging range of the succeeding sub-pixel block. For example, assuming that the ranging range of the distance measurement system is 0.5m (meter) to 100m, when each pixel block includes two sub-pixel blocks, if the two sub-pixel blocks are sequentially arranged in an increasing order of size, the ranging ranges of the two sub-pixel blocks may be 0.5m to 3m and 3m to 100m, respectively, and if the two sub-pixel blocks are sequentially arranged in a decreasing order of size, the ranging ranges of the two sub-pixel blocks may be 3m to 100m and 0.5m to 3m, respectively; similarly, when each pixel block includes three sub-pixel blocks, if the three sub-pixel blocks are sequentially arranged according to the increasing order of the sizes, the ranging ranges of the three sub-pixel blocks may be respectively 0.5m to 3m, 3m to 10m, and 10m to 100m, and if the three sub-pixel blocks are sequentially arranged according to the decreasing order of the sizes, the ranging ranges of the three sub-pixel blocks may be respectively 10m to 100m, 3m to 10m, and 0.5m to 3 m.
In one embodiment, the aperture distance between two diaphragms corresponding to any two adjacent sub-pixel blocks in each pixel block is equal to the parallax corresponding to the lower limit value of the ranging range of the distance measurement system. For example, assuming that the lower limit value of the range measurement range of the distance measurement system is 0.5m, the aperture pitch between two diaphragms corresponding to any adjacent two sub-pixel blocks in each pixel block is equal to 480 μm (micrometers).
In application, the target may be any object in free space. At least part of the pulse beams emitted to the target by the emitter are reflected to the collector by the target, so that the collector can collect the pulse beams reflected by the target and carry out photoelectric conversion to obtain corresponding photon signals, and then the photon signals are output to the control and processing circuit. The control and processing circuit synchronously sends a trigger signal to the emitter and the collector so as to synchronously trigger the emitter to emit a pulse beam and the collector to collect the pulse beam reflected by the target. The trigger signal may be a clock signal, and the clock signal for triggering the transmitter to transmit the pulse beam to the target may be defined as a start clock signal. The control and processing circuit obtains the time of flight of the pulsed light beam by calculating the time required for the pulsed light beam to be emitted until collected. In particular, the control and processing circuit may calculate the time interval between its emission of the start clock signal and its reception of the photon signal, which is the time of flight. Further, the distance of the target can be calculated according to the flight time, and the calculation formula is as follows:
D＝c*t/2；
where D represents the distance of the target, c represents the speed of light, and t represents the time of flight.
In application, the emitter comprises a light source unit comprising at least one light source. The Light source may be a Light Emitting Diode (LED), a Laser Diode (LD), an Edge Emitting Laser (EEL), a Vertical Cavity Surface Emitting Laser (VCSEL), or the like. The number of the light sources included in the light source unit can be set according to actual needs, and the light source unit can be a one-dimensional or two-dimensional light source array composed of at least two light sources. The light source array may be a vertical cavity surface emitting laser array chip formed by generating a plurality of vertical cavity surface emitting lasers on a single semiconductor substrate, and the arrangement of the light sources in the light source array may be regular or irregular. The pulsed light beam emitted by the light source may be visible light, infrared light, ultraviolet light, or the like.
In one embodiment, the transmitter further includes a driver for controlling the light source unit to transmit the pulse beam to the target at a preset frequency or a preset pulse period, the preset frequency and the preset pulse period being set according to a ranging range of the distance measuring system, the driver being connected to the light source unit.
In application, the light source unit emits a pulsed light beam to a target under the control of a driver. It will be appreciated that the light source unit may also be controlled to emit a pulsed light beam by means of a part of the control and processing circuitry or other circuitry present independently of the control and processing circuitry. The preset frequency is positively correlated with the range of the distance measuring system, and the preset pulse period is negatively correlated with the range of the distance measuring system.
In one embodiment, the transmitter further includes a first optical element for optically modulating the pulse beam emitted from the light source unit and projecting the modulated pulse beam to the target.
In applications, the optical modulation may be diffraction, refraction, reflection, etc., and the modulated pulsed light beam may be a focused light beam, a flood light beam, a structured light beam, etc. The first optical element may include at least one of a lens, a liquid crystal element, a diffractive optical element, a microlens array, a super surface (Metasurface) optical element, a mask plate, a mirror, a Micro-Electro-Mechanical System (MEMS) galvanometer, and the like.
Fig. 1 schematically shows that the transmitter 1 comprises a light source unit 11, a first optical element 12 and a driver 13, the light source unit 11 being connected to the driver 13.
In application, the collector comprises a pixel unit, wherein the pixel unit comprises at least one pixel block, and each pixel block comprises at least two sub-pixel blocks. The pixel unit is a pixel array composed of a plurality of Single Photon Avalanche photodiodes (SPADs), the Single Photon Avalanche photodiodes can respond to incident Single photons and output signals indicating the Time when the photons reach the Single Photon Avalanche photodiodes, and the weak light signals are acquired and the flight Time is calculated by using a Time-Correlated Single Photon Counting method (TCSPC), for example.
In application, the collector further includes at least one of a signal amplifier, a Time-to-Digital Converter (TDC), an Analog-to-Digital Converter (ADC), and the like connected to the pixel unit. These devices may be integrated with the pixel cell or may be part of the control and processing circuitry.
In one embodiment, the collector further comprises a second optical element for focusing the pulsed light beam reflected by the target to the pixel unit.
In one embodiment, the second optical element comprises at least one attenuation sheet, each attenuation sheet corresponds to a sub-pixel block with a measurement distance smaller than a distance threshold, and each attenuation sheet is used for attenuating the light intensity of the pulse light beam incident to the corresponding sub-pixel.
In one embodiment, the second optical element further comprises an imaging lens for image focusing of the pulsed light beam before incidence on the at least two diaphragms.
In one embodiment, the second optical element further comprises at least two first focusing lenses, each first focusing lens corresponding to one sub-pixel block, each first focusing lens being configured to focus the pulse beam shaped by the diaphragm to its corresponding sub-pixel block.
In application, the second optical element may include an imaging lens, and an aperture, a first focusing lens and a microlens array which are arranged in sequence and equal in number to all the sub-pixel blocks, and may further include an attenuation sheet corresponding to each sub-pixel block whose measurement distance is smaller than a distance threshold. The micro lens array comprises second focusing lenses with the number equal to the total number of pixels of all the sub pixel blocks, one first focusing lens corresponds to one sub pixel block, and one second focusing lens corresponds to one pixel in the sub pixel block. Each first focusing lens is used for focusing the pulse light beams reflected by the target and subjected to imaging focusing through the imaging lens to a plurality of second focusing lenses corresponding to the sub-pixel blocks when the target is located in the range measurement range of the corresponding sub-pixel block, and each second focusing lens is used for focusing the pulse light beams received by the second focusing lens to the corresponding pixel.
In application, because the intensity of a pulse light beam reflected by a target at a close distance is high and the number of photons is large, a photon pile-up effect (photo pile-up effect) is easily caused, an attenuation sheet needs to be arranged to attenuate the light intensity so as to solve the problem. By setting the attenuation slices with proper attenuation coefficients, the corresponding sub-pixel blocks of each attenuation slice can generate effective photon signals for calculating the flight time of the pulse light beam.
In one embodiment, the second optical element further includes a filter unit for filtering out background light and stray light incident to all the pixel blocks, the filter unit being disposed between the imaging lens and the first lens. The filtering unit may be a low pass filter.
The collector 2 is shown in fig. 1 by way of example as comprising a pixel element 21, a filter element 22 and a second optical element 23. It should be understood that the filter unit 22 is disposed between the pixel unit 21 and the second optical element 23 in fig. 1 for convenience of illustration, and is not used to limit the relative positions of the filter unit 22 and the second optical element 23 in practical applications.
The second optical element exemplarily shown in fig. 3 includes an imaging lens 231, two first focusing lenses 232 and 233, and a microlens array including a plurality of second focusing lenses 234, the first focusing lens 232 corresponding to the sub-pixel block 211, the first focusing lens 233 corresponding to the sub-pixel block 212, and each of the second focusing lenses 234 corresponding to each of the pixels 2121, respectively; the filter unit 22 is disposed between the imaging lens 231 and the first and second diaphragms 241 and 242; an attenuation sheet 235 is disposed between the second focusing lens and the first focusing lens 232 corresponding to the sub-pixel block 211.
In one embodiment, the single photon avalanche photodiode responds to incident single photon to output photon signal, and the control and processing circuit receives the photon signal and performs signal processing to obtain the flight time of the optical signal reflected by the target. Specifically, the control and processing circuitry calculates the number of photon signals collected to form successive time cells (bins) that are joined together to form a statistical histogram for reconstructing a time series of optical signals reflected by the target, and identifies the time of flight of the optical signals reflected by the target from being transmitted to being received using peak matching and filtering detection. The control and Processing Circuit may be a Central Processing Unit (CPU), other general purpose Processor, System-on-a-Chip (SOC), Digital Signal Processor (DSP), Application Specific Integrated Circuit (ASIC), Field-Programmable Gate Array (FPGA) or other Programmable logic device, discrete Gate or transistor logic device, discrete hardware Array, etc. A general purpose processor may be a microprocessor or any conventional processor or the like.
In one embodiment, the distance measurement system further comprises a memory for storing a pulse encoding program. The driver is connected with the memory and is used for controlling the excitation time, the emission frequency and the like of the light source unit for emitting the pulse light beam by using a pulse code program.
In one embodiment, the distance measurement system may further include at least one of an RGB camera, an infrared camera, and an Inertial Measurement Unit (IMU) for implementing functions such as 3D texture modeling, infrared face recognition, time localization and mapping (SLAM).
In one embodiment, the control and processing circuitry comprises:
the TDC circuits are equal to all the sub-pixel blocks in number, each TDC circuit is connected with one sub-pixel block, and each TDC circuit is used for calculating the flight time according to the photon signals output by the sub-pixel blocks connected with the TDC circuit and converting the flight time into time codes; or, TDC circuits with the same number as the total pixels of all the sub-pixel blocks, each TDC circuit is connected with one pixel and is used for calculating the flight time according to the photon signals output by the pixels connected with the TDC circuit and converting the flight time into time codes;
the histogram circuits are used for storing time codes output by all the TDC circuits connected with the histogram circuits and generating a histogram according to the time codes stored in at least one pulse period of the pulse light beam, the flight time of the pulse light beam is determined based on the histogram, and the histogram is used for representing the waveform of the pulse light beam reflected by the target.
Fig. 4 exemplarily shows on the basis of fig. 2 that the control and processing circuit 3 includes a first TDC circuit 311, a second TDC circuit 312, …, and a mTDC circuit 31m connected in one-to-one correspondence with the first sub-pixel block 211, the second sub-pixel block 212, …, and the mth sub-pixel block 21m in one pixel block 20, and further includes a histogram circuit 32 connected to the first TDC circuit 311, the second TDC circuit 312, …, and the mTDC circuit 31 m.
In application, all TDC circuits included in the control and processing circuit may form an array circuit, and each TDC circuit is correspondingly connected to a sub-pixel block or a pixel. The TDC circuit is used for calculating the flight time of the pulse beam, namely the time difference between the receiving time and the transmitting time according to the receiving time of the received photon signal and the transmitting time of the pulse beam transmitted to the target by the transmitter, converting the flight time into a time code and storing the time code in a histogram circuit connected with the time code, wherein the time code can be a temperature code or a binary code, and the target is a target located in the range measurement range of a sub-pixel block connected with the TDC circuit. The histogram circuit is used for drawing a time code saved by the distance testing system after at least one measurement is finished into a histogram which can represent the waveform of the pulse light beam reflected by the target, and the time of each measurement is at least one pulse period of the pulse light beam.
In one embodiment, the time width of each TDC circuit is positively correlated with the measured distance of its connected sub-pixel block, and the time resolution of each TDC circuit is negatively correlated with the measured distance of its connected sub-pixel block.
In one embodiment, the time code is a temperature code or a binary code.
In application, the time width of the TDC circuit is affected by the measurement distance of the connected sub-pixel block, the time resolution of the TDC circuit affects the measurement accuracy of the distance measurement system, and the more the number of bits of the time code output by the TDC circuit is, the higher the requirement on the storage capacity of the connected histogram circuit is. In order to reduce the data storage amount, reduce the consumption of the storage space of the histogram circuit, and save the cost, the time width and the time resolution of each TDC circuit need to be reasonably set, so that the time width of the TDC circuit connected to the sub-pixel block with the smaller measurement distance is smaller than the time width of the TDC circuit connected to the sub-pixel block with the larger measurement distance, and the time resolution of the TDC circuit connected to the sub-pixel block with the smaller measurement distance is higher than the time resolution of the TDC circuit connected to the sub-pixel block with the larger measurement distance. For example, when the ranging range of the sub-pixel block is 0.3m to 3m, the time resolution of the TDC circuit connected thereto is 125 picoseconds (ps); when the ranging range of the sub-pixel block is 3m to 100m, the time resolution of the TDC circuit connected with the sub-pixel block is 0.5 nanoseconds (ns). The histogram circuit forms a histogram having different time cell widths according to a time code (time code) output from each TDC circuit connected thereto, and the time cell width is determined by the time resolution of the TDC circuit.
In one embodiment, among all the TDC circuits electrically connected to one of the pixel blocks, the TDC circuits connected to the sub-pixel block having the large measurement distance have a time of turning on later than the TDC circuits connected to the sub-pixel block having the small measurement distance.
In application, for the sub-pixel block with a larger measurement distance, the transmission time of the pulse beam reflected by the target is longer due to the longer distance of the measured target, so that the starting time of the TDC circuit connected with the sub-pixel block can be delayed for a certain time relative to the starting clock signal.
In one embodiment, the starting time of all TDC circuits connected with one pixel block is delayed in sequence according to the increasing order of the measuring distance of the sub-pixel blocks; the starting time of the first TDC circuit is synchronous with the emission time of the pulse beam, and the delay time of the starting time of other TDC circuits relative to the emission time is greater than or equal to the flight time corresponding to the lower limit value of the ranging range of the sub-pixel block connected with the TDC circuit.
In application, the start time of the TDC circuit connected to the sub-pixel block with the smallest measurement distance in each pixel block is synchronized with the start clock signal (i.e. the emission time of the pulse beam), the start times of the other TDC circuits are sequentially delayed relative to the start clock signal, the delay time of each TDC circuit can be determined according to the flight time corresponding to the lower limit value of the ranging range of the sub-pixel block connected to the TDC circuit, for example, the ranging range of the sub-pixel block connected to one TDC circuit is 3m-100m, the delay time of the TDC circuit can be set to the flight time corresponding to the lower limit value of 3m, i.e. 3m/c is 20ns, when the histogram circuit is plotted according to the time code output by the TDC circuit, the histogram circuit starts to plot from the time unit corresponding to the delay time of 20ns relative to the start clock signal.
In one embodiment, the sub-pixel blocks with the size larger than the preset size threshold include blank areas with no pixels, and the blank areas are arranged in non-edge areas of the sub-pixel blocks where the sub-pixel blocks are located or areas adjacent to other sub-pixel blocks.
In application, as the larger the size of the sub-pixel block is, the more pixels are included, so that in order to reduce the number of pixels in the sub-pixel block with the larger size, a blank region may be provided in the sub-pixel block, thereby reducing the number of the optical sub-signals received by the TDC circuit connected to the sub-pixel block, and correspondingly, reducing the storage capacity of the histogram circuit that needs to be consumed, so that the histogram circuit may use a storage with a smaller memory, and by reducing the number of pixels in the sub-pixel block, the difficulty in integrating the single sub-pixel block may be reduced.
Fig. 5 exemplarily shows that one pixel block 20 includes a first sub-pixel block 211 and a second sub-pixel block 212, the first sub-pixel block 211 includes 3 × 3 pixels, the second sub-pixel block 212 includes a blank region 2121 and 3 × 6 pixels, and the blank region 2121 is disposed in a region where the first sub-pixel block 211 is adjacent to the second sub-pixel block 212.
Fig. 6 exemplarily shows that one pixel block 20 includes a first sub-pixel block 211 and a second sub-pixel block 212, the first sub-pixel block 211 includes 3 × 3 pixels, the second sub-pixel block 212 includes 3 × 8 pixel regions, the pixel regions of the second column, the fourth column and the sixth column in the second row in the second sub-pixel block 212 are not provided with pixels, and the remaining pixel regions are provided with pixels.
In one embodiment, the emitter includes at least two light source columns sequentially shifted by a first distance in a preset direction (e.g., a vertical direction), each light source column includes at least two light sources sequentially arranged in the preset direction, and a distance between two adjacent light sources in each light source column in the preset direction is greater than or equal to a second distance;
the collector comprises at least two pixel columns which are sequentially shifted by a first distance in a preset direction, each pixel column comprises at least two pixel blocks which are sequentially arranged in the preset direction, and the distance between two adjacent pixel blocks in each pixel column in the preset direction is greater than or equal to a second distance;
the distance measurement system is placed in the horizontal plane, the preset direction is the vertical direction, the first distance is larger than or equal to the diameter of the light source, and the second distance is larger than or equal to the product of the total number of light source columns included by the emitter and the first distance.
In application, the preset direction can be defined as any direction according to actual needs, when the distance measuring system is placed on a horizontal plane, the preset direction is the vertical direction perpendicular to the horizontal plane, and no matter how the distance measuring system is placed, the preset direction is perpendicular to the plane on which the distance measuring system is placed.
In application, the first distance may be set to any value larger than or equal to the diameter of the light source according to actual needs, and the second distance may be set to any value larger than or equal to the product of the total number of light source columns included in the emitter and the first distance according to actual needs. The arrangement of the light source units can be understood as that at least one light source is inserted between adjacent light sources of one light source column to form the light source column with more light sources and uniform distribution, so that the pulse light beams projected to the target by the light source units form continuous scanning lines of light spots. By increasing the distance between the adjacent light sources in the single light source column, the crosstalk between the pulse light beams emitted by the adjacent light sources can be effectively reduced; the target is rotationally scanned by arranging at least two light source columns to obtain a point cloud picture, and the rotational scanning resolution ratio relative to one light source column is higher; and under the condition that the areas of the pixel units are the same, at least two light source columns are arranged, so that the number of light sources in each light source column can be reduced, the manufacturing difficulty of the light source units is reduced, a larger field of view can be obtained in a preset direction, and the measurement frame rate of the distance measurement system is improved.
The light source unit 11 exemplarily shown in fig. 7 includes three light source arrays 101, 102 and 103, each including 6 light sources 10, and correspondingly, the pixel unit 21 also includes three pixel arrays 201, 202 and 203, each including 6 pixel blocks 20, a distance between two adjacent light sources 10 is d, and the first distance is d/3.
In one embodiment, the distance measuring system further comprises a rotating base, and the emitter and the collector are mounted on the rotating base, so that the emitter and the collector can rotate and scan under the control of the control and processing circuit to realize distance measurement of the target in a large 360-degree field of view.
The swivel base 4 is shown in fig. 7 by way of example.
The embodiment of the present application further provides a distance measurement method implemented based on the distance measurement system 100, including:
controlling the transmitter to transmit a pulse beam to the target;
controlling each sub-pixel block of an acquisition device to acquire photons in the pulse light beams shaped by the corresponding diaphragm of the acquisition device and output photon signals, wherein the acquisition device comprises at least one pixel block and at least two diaphragms, each pixel block comprises at least two sub-pixel blocks which are sequentially arranged according to the increasing or decreasing order of the size, one sub-pixel block corresponds to one diaphragm, the size and the measurement distance of each sub-pixel block are positively correlated and negatively correlated with the aperture of the corresponding diaphragm, and each diaphragm is used for shaping the pulse light beams reflected by the target in the range-measuring range of the corresponding sub-pixel block;
calculating the time of flight of the pulsed light beam from the photon signal.
In one embodiment, said calculating time of flight of said pulsed light beam from said photon signal comprises:
respectively calculating flight time according to the photon signals output by each sub-pixel block and converting the flight time into time codes;
saving all the time codes and generating a histogram according to the time codes saved in at least one period of the pulse light beam, and determining the flight time of the pulse light beam based on the histogram, wherein the histogram is used for representing the waveform of the pulse light beam reflected by the target.
In an application, the distance measuring method may be performed by the control and processing circuit when running a computer program stored in the control and processing circuit or in the memory.
An embodiment of the present application further provides a computer-readable storage medium, where a computer program is stored, and when the computer program is executed by a processor, the steps in the above distance measurement method embodiment are implemented.
Embodiments of the present application provide a computer program product, which, when running on a distance measurement system, causes the distance measurement system to perform the steps in the above distance measurement method embodiments.
The embodiment of the application transmits a pulse beam to a target through a transmitter; the collector comprises at least one pixel block and at least two diaphragms, each pixel block comprises at least two sub-pixel blocks which are sequentially arranged according to the increasing or decreasing order of the size, one sub-pixel block corresponds to one diaphragm, the size and the measuring distance of each sub-pixel block are positively correlated and negatively correlated with the aperture of the corresponding diaphragm, each diaphragm is used for shaping pulse beams reflected by a target in the range-measuring range of the corresponding sub-pixel block, and each sub-pixel block is used for collecting photons in the pulse beams shaped by the corresponding diaphragm and outputting photon signals; by connecting the control and processing circuit with the emitter and the collector respectively and calculating the flight time of the pulse light beam according to the photon signals, the accurate measurement of the distances between different targets positioned at least two measuring distances and the distance measuring system can be realized, and the measuring error is effectively reduced.
In the above embodiments, the descriptions of the respective embodiments have respective emphasis, and reference may be made to the related descriptions of other embodiments for parts that are not described or illustrated in a certain embodiment.
Those of ordinary skill in the art will appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware or combinations of computer software and electronic hardware. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present application.
The above-mentioned embodiments are only used for illustrating the technical solutions of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications and substitutions do not substantially depart from the spirit and scope of the embodiments of the present application and are intended to be included within the scope of the present application.
Claims (10)
1. A distance measuring system, comprising:
a transmitter for transmitting a pulsed light beam to a target;
the collector comprises at least one pixel block and at least two diaphragms, each pixel block comprises at least two sub-pixel blocks which are sequentially arranged according to the ascending or descending order of the size, one sub-pixel block corresponds to one diaphragm, the size and the measuring distance of each sub-pixel block are positively correlated and negatively correlated with the aperture of the corresponding diaphragm, each diaphragm is used for shaping pulse beams reflected by a target in the range-measuring range of the corresponding sub-pixel block, and each sub-pixel block is used for collecting photons in the pulse beams shaped by the corresponding diaphragm and outputting photon signals;
and the control and processing circuit is respectively connected with the emitter and the collector and is used for calculating the flight time of the pulse light beam according to the photon signal.
2. The distance measuring system of claim 1, wherein the collector further comprises at least one attenuation sheet, each attenuation sheet corresponds to a sub-pixel block with a measuring distance smaller than a distance threshold, and each attenuation sheet is used for attenuating the light intensity of the pulse light beam incident to its corresponding sub-pixel.
3. The distance measuring system of claim 2, wherein the collector further comprises an imaging lens for imaging and focusing the pulse beam reflected by the target before the pulse beam reflected by the target is incident on the diaphragm.
4. The distance measurement system of claim 1 wherein the collector further comprises at least two first focusing lenses, each first focusing lens corresponding to one of the sub-pixel blocks, each first focusing lens for focusing the pulse beam shaped by the diaphragm to its corresponding sub-pixel block.
5. The distance measurement system of claim 1 wherein said collector further comprises a filtering unit for filtering out background and stray light incident to said at least one block of pixels.
6. The distance measurement system according to claim 1, wherein an aperture distance between two diaphragms corresponding to any adjacent two sub-pixel blocks in each of the pixel blocks is equal to a parallax corresponding to a lower limit value of a range of the distance measurement system.
7. The distance measurement system of any of claims 1 to 6 wherein said control and processing circuitry includes a number of TDC circuits equal to all of said sub-pixel blocks, each said TDC circuit being connected to one of said sub-pixel blocks, the time width of each said TDC circuit being positively correlated with the measured distance of its connected sub-pixel block, the time resolution of each said TDC circuit being negatively correlated with the measured distance of its connected sub-pixel block.
8. The distance measurement system according to any one of claims 1 to 6, wherein the transmitter includes at least two light source columns sequentially shifted by a first distance in a preset direction, each of the light source columns includes at least two light sources sequentially arranged in the preset direction, and a distance between two adjacent light sources in each of the light source columns in the preset direction is greater than or equal to a second distance;
the collector comprises at least two pixel columns which are sequentially shifted by a first distance in a preset direction, each pixel column comprises at least two pixel blocks which are sequentially arranged in the preset direction, and the distance between two adjacent pixel blocks in each pixel column in the preset direction is greater than or equal to a second distance;
the preset direction is a vertical direction when the distance measuring system is placed on a horizontal plane, the first distance is larger than or equal to the diameter of the light source, and the second distance is larger than or equal to the product of the total number of light source columns included by the emitter and the first distance.
9. A distance measuring method, characterized by comprising:
controlling the transmitter to transmit a pulse beam to the target;
controlling each sub-pixel block of an acquisition device to acquire photons in the pulse light beams shaped by the corresponding diaphragm of the acquisition device and output photon signals, wherein the acquisition device comprises at least one pixel block and at least two diaphragms, each pixel block comprises at least two sub-pixel blocks which are sequentially arranged according to the increasing or decreasing order of the size, one sub-pixel block corresponds to one diaphragm, the size and the measurement distance of each sub-pixel block are positively correlated and negatively correlated with the aperture of the corresponding diaphragm, and each diaphragm is used for shaping the pulse light beams reflected by the target in the range-measuring range of the corresponding sub-pixel block;
calculating the time of flight of the pulsed light beam from the photon signal.
10. A computer-readable storage medium, in which a computer program is stored which, when being executed by a processor, carries out the steps of the distance measuring method according to claim 8.
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