CN108387906A - A kind of three-dimensional laser imaging system based on FPGA-TDC - Google Patents
A kind of three-dimensional laser imaging system based on FPGA-TDC Download PDFInfo
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- CN108387906A CN108387906A CN201810023421.4A CN201810023421A CN108387906A CN 108387906 A CN108387906 A CN 108387906A CN 201810023421 A CN201810023421 A CN 201810023421A CN 108387906 A CN108387906 A CN 108387906A
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- tdc
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- imaging system
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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
- G01S17/88—Lidar systems specially adapted for specific applications
- G01S17/89—Lidar systems specially adapted for specific applications for mapping or imaging
Abstract
The present invention proposes a kind of three-dimensional laser imaging system based on FPGA TDC.Laser beam is divided into reference beam and transmitting light beam through light splitting piece.Reference beam generates reference signal through single-point APD reference sensors.Transmitting light beam is collected through optical lens, is imaged on the APD area array sensors of focal plane, and the roads n echo-signal is generated.Each TDC measurement modules that reference signal and echo-signal are realized in FPGA measure, and generate TDC data.TDC data, thick chronometric data and mark are written to by data simultaneous module control in asynchronous FIFO together, and data reading is sent to host computer by communication module, by host computer using flight time algorithm and related correction algorithm, obtains the depth image of object.The present invention be suitable for large area array three-dimensional laser imaging system inexpensive, quick exploitation, can obtain faster high-precision, high frame frequency object depth image.
Description
Technical field
The present invention relates to a kind of laser active illuminations three of time-to-digital converter (TDC) that realizing measured signal based on FPGA
Imaging system is tieed up, a kind of method that TDC data synchronize reading is further related to, belongs to technique of laser imaging field.
Background technology
The 3-D imaging system of laser pulse active illumination is by emitting laser beam to target surface, passing through optical system
Collect the irreflexive return laser beam of target surface, calculate time difference of each location of pixels from Laser emission to return build with
Distance is the three-dimensional image forming apparatus of the depth image of unit.Since the monochromaticjty of laser, coherence, directionality and high brightness are special
Sign, laser pulse three-dimensional imaging can realize high frame per second, high-resolution, obtain the depth information of target, be suitable for over the horizon at
Picture, and remove camouflage ability with certain.Therefore, laser three-dimensional imaging system is in military surveillance, remotely sensed image, unmanned vapour
Vehicle etc. is multi-field to have wide practical use, and is a current international and domestic important research direction.
The method for obtaining Laser emission to the time difference returned is known as time-of-flight method (Time ofFlight), influences to fly
In many physical quantitys of row time range accuracy, the most key parameter is the flight time of light.Currently, carrying out flight time survey
It is m- number conversion (TDC) function when special integrated chip (ASIC) is realized that the method for amount, which mainly has two major classes, one kind, separately
One kind is to realize TDC functions using existing resource on programmable gate array (FPGA).
Although TDC chip functions are perfect, easy to use, monolithic channel number is insufficient, is needed when large area array uses a large amount of
Chip does not have the advantage of using.The use of FPGA deployment is more quickly that cost performance is higher currently, in large area array imaging system
Implementation.FPGA can be used as system Control ＆ data acquisition processor simultaneously, increase processor without additional, when saving exploitation
Between and hardware cost.
Invention content
The present invention devises a kind of laser active illumination 3-D imaging system based on FPGA-TDC, and proposes a kind of TDC
Data synchronize the method read, avoid when echo-signal is excessive, and data volume is excessive to cause congestion, and then generates valid data and lose
The case where mistake.
The present invention is achieved by the following technical solutions.
The system is by APD area array sensors, single-point APD reference sensors, laser pulse emission device, FPGA boards, upper
The compositions such as machine processing terminal and power supply.The FPGA boards implement function such as module：Measured signal TDC measurement modules, reverse phase
Device group, Clock management module (DCM), Laser emission control module, thick timing module, TDC data acquisition modules and host computer are logical
Interrogate module etc..The measured signal TDC measurement modules include following function module：Time delay chain module, data collection synchronous module,
Asynchronous FIFO module.Optical device includes 1:9 light splitting pieces, reception camera lens, cylindrical mirror etc..
Host computer controls the laser pulse emission device by sending control instruction by the Laser emission control module
Transmitting stops.Control instruction further includes the frequency and pulse width information of laser pulse, and the Laser emission control module carries in real time
These information are taken, change the frequency and pulsewidth of laser pulse in real time, to reach control laser pulse repetition frequency and launch energy
The purpose of amount, with the use demand suitable for different distance, different frame rates imaging.The laser of the laser pulse emission device transmitting
After cylindrical mirror shaping described in Shu Jing, pass through 1:9 light splitting pieces are divided into reference beam and transmitting light beam.The reference beam is by the list
Point APD reference sensors are collected, and are generated reference signal, are measured for TDC measurement modules in the FPGA, to obtain reference
TDC data.The transmitting light beam is collected through target surface diffusing reflection through system optical lens, and the faces APD battle array passes on focal plane
It is imaged on sensor, generates the roads n echo-signal, measured through the TDC measurement modules, generate echo TDC data.It is to be appreciated that every
Road measured signal has a set of independent TDC measurement modules, different.It is described to refer to TDC data and the echo TDC numbers
According to, by the data collection synchronous module control by effective TDC data, thick chronometric data and mark (reference identification or position
Mark) it is stored in asynchronous FIFO jointly.The TDC data acquisition modules detect fifo status in real time by AXI buses, and cycle is read
The data of each FIFO are simultaneously sent to host computer by the Upper machine communication module.The thick timing module is configured to 16
Cycle tiemr provides relative time stamp for each TDC data.The host computer processing terminal, is referred to and echo data
Afterwards, using flight time algorithm and corresponding correction algorithm, the depth image of object is obtained.
The depth image that the TDC data obtained obtain object by flight time algorithm is measured, specific method describes such as
Under.
Clock cycle T is subdivided into n parts by time delay chain, each tap output of time delay chain to d type flip flop, and when rising edge clock adopts
Collect tap data.When START signal arrives, when 0 rising edge of CLK clocks acquires, signal does not enter time delay chain, and clock 1 rises
When along acquisition, signal has propagated a distance in time delay chain, and m1 bit of tap output 1 is protected together with thick timing time stamp
Save as TDC data.Later, when STOP signals arrive, CLK clocks 2 do not collect data, when CLK clocks 3, tap output m2
Bit 1.
By handling TDC data in each pulse period, the depth information of each pixel, formula can be obtained
For：
L=k*T+ (m1-m2)*tdelay+C
C is the fixed error of circuit delay, and C values can be determined by calibration experiment.It can will be on signal path in addition, subtracting operation
Fractional error eliminate, improve measurement accuracy.
The flight time algorithm of the present invention only needs the leading edge time of measured signal, if input measured signal pulsewidth is wider
In the case of, other data measured are invalid data.Since in the case where pixel number is more, FPGA resource can not configure
Enough FIFO depths, if while to read FIFO frequencies insufficient, in a large amount of echo-signals, data congestion can be caused, to
Lose part effective information.
The present invention proposes a kind of method of data synchronization, for effective TDC data to be written to FIFO, shields invalid TDC
Data.Generating metastable phenomenon when due to avoid time delay chain tap output is connected to after needing two d type flip flops of series connection
FIFO, therefore, effective TDC data need to be written to FIFO in third rising edge clock.Data simultaneous module is used similar to before
Along the method for detection, after the arrival of effective TDC clocks, detect that state change, the FIFO that following clock generates a cycle are write
Signal, then third clock effective TDC data are synchronously written FIFO, do not generate write signal later, mask invalid data.
The beneficial effects of the invention are as follows：
The 3-D imaging system of the present invention realizes TDC functions by using FPGA, can realize high accuracy depth image measurement,
Such as use Kintex-7 serial, a delay unit delay 70ps, therefore theoretically up to the measurement accuracy of 70ps.Meanwhile it is whole
A system structure is simple and practical, and one-channel signal occupancy FPGA resource is few, is very suitable for large area array three-dimensional laser imaging device
Quickly exploitation.The present invention method of data synchronization, can effectively avoid in large area array in application, due to data volume it is excessive caused by
Data congestion, loss situation, while the data volume of host computer processing is decreased, depth image can be obtained faster.
Description of the drawings
Fig. 1 laser three-dimensional imaging system principle diagrams
Fig. 2 FPGA function module composition frame charts
Fig. 3 time flight algorithm sequence diagrams
Composition frame chart inside Fig. 4 TDC measurement modules
Specific implementation mode
Technical solution according to the present invention, those of ordinary skill in the art can imagine the present invention based on FPGA's
Many embodiments of three-dimensional laser imaging system.Therefore, detailed description below and attached drawing are only the technical sides of the present invention
The exemplary illustration of case, and be not to be construed as the whole of the present invention or be considered as the limitation or restriction to technical solution of the present invention.
Specific embodiments of the present invention are as follows：
Area array sensor uses the faces the APD battle array of the 905nm wave bands of 8x8 pixels.Back-end circuit is transported using electric current amplifier, voltage
It puts and comparator, generation can be by the digital signal of FPGA receiving.Single-point APD uses AD500-9, back-end circuit and area array sensor
It is identical.Laser uses PL90-3, and the 905nm pulsed infrared laser pipes of 75W peak powers, circuit includes power MOS pipe, MOS
Pipe driving chip, high speed capacitance etc..FPGA platform uses XilinxKintex-7XC7K325T-2FFG900.Optical device includes
9:1 light splitting piece, reception camera lens, cylindrical mirror etc..
Host computer by sending control instruction, the laser pulse emission device control the laser pulse emission device start or
It is stopped.The command information that host computer is sent further includes the frequency and pulse width information of laser-driven signal, the laser
Emission control module reads these information in real time, and then changes the frequency and pulse width of drive signal in real time, to which control swashs
The repetition rate and emitted energy of light.Achievable driving signal frequency and pulsewidth are as shown in the table, and frequency and pulsewidth be simultaneously in table
Non- one-to-one correspondence：
1 laser-driven signal of table
The laser beam of the laser pulse emission device transmitting passes through 1 after the cylindrical mirror shaping:9 light splitting pieces are divided into ginseng
Examine light beam and transmitting light beam.The reference beam is collected by the single-point APD reference sensors, reference signal is generated, for described
TDC measurement modules measure in FPGA, to obtain with reference to TDC data.The transmitting light beam, through target surface diffusing reflection,
It collects through system optical lens, is imaged on APD area array sensors on focal plane, generate the roads n echo-signal, surveyed through the TDC
It measures module to measure, generates echo TDC data.
TDC measurement modules use two clock domains, 0 ° and 180 °, clock frequency 400MHz.Each clock domain is single
Time delay chain needs 20 delay units.The inverted device group of input signal, the time delay chain module for being divided to two-way to be input to two clock domains
In measure.The TDC data of acquisition are stored under data simultaneous module control different together with thick clocking information and mark
Walk FIFO.Communication processor uses Microblaze soft-core processors, master clock frequency 100MHz.Asynchronous FIFO is total by AXI
Line realizes data connection with communication processor.Asynchronous FIFO writes clock 400MHz, reads clock 100Mz, 64 write-ins, 32 readings
Go out.Therefore, it is necessary to using data simultaneous module, invalid data is shielded.64 TDC data formats are as follows：
The thick timing module uses DSP hardware unit, is configured to 16 cycle tiemrs, is carried for each TDC data
It is stabbed for relative time.
The host computer communication module sends data to host computer using Ethernet.Host computer obtains the reference and returns
Wave number, using flight time algorithm and corresponding correction algorithm, obtains the depth image of object after.
Claims (4)
1. a kind of three-dimensional laser imaging system based on FPGA-TDC, it is characterised in that：
Host computer is controlled the transmitting of the laser pulse emission device by the Laser emission control module by sending control instruction
Or stop；The laser beam of the laser pulse emission device transmitting passes through 1 after the cylindrical mirror shaping:9 light splitting pieces are divided into reference
Light beam and transmitting light beam；The reference beam is collected by the single-point APD reference sensors, reference signal is generated, for described
TDC measurement modules measure in FPGA, to obtain with reference to TDC data；The transmitting light beam, through target surface diffusing reflection,
It collects through system optical lens, is imaged on APD area array sensors on focal plane, generate the roads n echo-signal, surveyed through the TDC
It measures module to measure, generates echo TDC data；It is to be appreciated that having a set of independent TDC measurement modules per road measured signal, mutually
It differs；It is described to refer to TDC data and the echo TDC data, it is controlled effective TDC numbers by the data collection synchronous module
It is stored in asynchronous FIFO jointly according to, thick chronometric data and mark (reference identification or station location marker)；The TDC data acquisition modules
Fifo status is detected in real time by AXI buses, and cycle reads the data of each FIFO and sent out by the Upper machine communication module
It send to host computer；The host computer processing terminal after obtaining reference and echo data, utilizes flight time algorithm and corresponding correction
Algorithm obtains the depth image of object.
2. a kind of three-dimensional laser imaging system based on FPGA-TDC according to claim 1, wherein：
The information that laser pulse frequency and pulsewidth are controlled in the Laser emission control module extract real-time control instruction, to real
When control laser pulse repetition frequency and emitted energy, with the use demand suitable for different distance, different frame rates imaging.
3. a kind of three-dimensional laser imaging system based on FPGA-TDC according to claim 1, wherein：
The thick timing module is configured to 16 cycle tiemrs, and relative time stamp is provided for each TDC data.
4. a kind of three-dimensional laser imaging system based on FPGA-TDC according to claim 1, wherein：
The method that the data collection synchronous module uses similar leading edge detection, the third clock after effective TDC clocks will
Effective TDC data are synchronously written FIFO, mask invalid data.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111007520A (en) * | 2019-12-30 | 2020-04-14 | 中国科学院微电子研究所 | Multi-channel time measuring system and method based on FPGA and laser scanner |
| CN112771408A (en) * | 2020-01-20 | 2021-05-07 | 深圳市速腾聚创科技有限公司 | Time-of-flight measurement method and device, storage medium and laser radar |
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| CN111007520A (en) * | 2019-12-30 | 2020-04-14 | 中国科学院微电子研究所 | Multi-channel time measuring system and method based on FPGA and laser scanner |
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