Lidar: Look to drive automatically from photoelectricity technology angle

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Lidar and the sensor technology that compete to it (camera, radar and ultrasonic) the need that reinforced pair of sensor confluence, also chose photoelectricity detector, illuminant and MEMS Zhen Jing to raise taller requirement to serious and careful ground. Sensor technology, into resemble, radar, optical exploration technology and range finding technology (lidar) , the progress of electronic technology and artificial intelligence, make tens of planting advanced driver support system (ADAS) be able to come true, include to prevent bump, scotoma is monitored, driveway deviate early-warning and jockey auxiliary etc. The synchronism that implements these systems through sensor confluence moves, can let the car surveillance surroundings that drives completely automatically, warn the driver's potential road risk, take independence even at the driver avoid the action to collide in order to prevent. Drive automatically to the car still must distinguish below high speed condition and distinguish the object of ahead. Adopt range finding technique, these drive automatically car must fast compose builds one Zhang Yao 100m inside the distance three-dimensional (3D) map, be in be as high as 250m to be apart from the image that tall horn resolution establishs inside limits. If the driver is not attendant, the artificial intelligence of car must make optimal and decision-making. Finish one of a few kinds of of this one task basic methods, measure energy pulse namely from drive automatically the time of flight going there and back that car returns vehicle again to the target (ToF) . Should know " pulse " when carrying airy rate, can calculate the distance that nods to reflection -- pulse can be ultrasonic (sonar) , radio wave (radar) or smooth (lidar) . In technology of these 3 kinds of ToF, lidar is the optimal alternative that offers picture of taller angle resolution, because it has smaller diffractive character and diverge of beam of light to spend, can distinguish photograph adjacent object better than microwave radar. Resolution of this kind of tall angle is attached most importance to especially below high speed should, can offer enough time to answer potential risk, if collide head on. The choice of laser illuminant is in ToF lidar, laser launchs duration to be the pulse of τ , spark in emissive instant the in-house clock in time circuit (later development has graphic representation) . From target catoptric smooth pulse arrives at photoelectricity detector, changeover produces telegraphic date to output outdated bell to stop to time. This kind of way that measures time of T of Δ of ToF going there and back can be calculated the distance R that nods to reflection. If laser and photoelectricity detector are located in same position actually, be apart from decide by next formula: C is the velocity of light in vacuum in, the refractive index that N is transmission medium (it is about to air 1) , the influence is apart from the element of resolution Δ R to have two: The bring about dimensional error W that the inaccuracy when measuring Δ T spends δ Δ T and pulse width surely (τ of C of W = ) . Represent range finding resolution with the first element 1 / of Δ R = τ of Δ of 2 C δ , and represent range finding resolution with the 2nd 1 / of Δ R = 1 / of = of 2 W 2 C τ . If measure an interval with the resolution of 5cm, afore-mentioned relation mean δ Δ T to be 300ps about respectively, τ is 300ps about. Detector of photoelectricity of requirement of flight time lidar and ever since electronics system has very little time to shake (the main contribution element of δ Δ τ ) and the pulse laser that can shoot wide time of short arteries and veins, for example relatively costly leather second laser. At present the laser in typical car lidar system produces the pulse that makes an appointment with 4ns duration, reducing diverge of beam of light so is necessary. Diverge of beam of light depends on wavelengh and emissive antenna dimension (microwave radar) or lenticular aperture size (lidar) ratio. Microwave radar this one specific value is greater, accordingly disperse the internal heat with sudorifics is spent bigger, angle resolution is inferior. Radar of the microwave in the graph (black) will not distinguish these two cars, and lidar (gules) can. To architect of car lidar system, one of the most crucial choices are smooth wavelengh. The element that restricts this one choice has a few: · is in to the security · of human vision the usability of the transmits characteristic · laser usability in atmosphere and photoelectricity detector two kinds of the most popular wavelengh are 905 with 1550 Nm, the main good point of 905nm is silicon absorbs photon in this good qualities, and the indium gallium arsenic that detector of silicon radical photoelectricity compares smooth place of exploration 1550 Nm to need normally (InGaAs) close infra-red detector is cheap. Can use at driving automatically of lidar bank the MPPC outside Song Jingong (silicon photoelectricity times add a canal) , taller exploration efficiency is had in 905nm place, answer speed fast, working temperature range is wide, suit the lidar application below all sorts of circumstances, the long distance that uses method of TOF range finding especially is measured. However, the human vision safety of 1550nm is spent taller, can use the laser that bigger radiant energy measures odd pulse -- a this is light-wave long choice main factor. 1550nm detector bank attenuation of air of loose InGaAs APD G8931 (fall in all weather condition) , the reflectivity of the scattering of the particle in air and target surface is concerned with wavelengh. Because have the weather condition of various likelihood and reflection face, a complex issue is for the alternative that leaves car lidar wavelengh to these conditions. Below most actual condition, the smooth loss that 905 Nm locates is smaller, because be in,905 Nm place wants the specific absorption of the moisture of 1550 Nm place big. The chooses to only one fraction pulse blasts off photon of smooth detector can reach the valid area of photoelectricity detector. If method of pulse of atmosphere attenuation edge is indeclinable, diverge of laser light beam is spent can ignor, facula dimension is less than a target, an angle of incidence is perpendicular at detector and reflector is lambert body (all square Xiang Jun is reflexed) , receive P of peak value power solely (R) for: P0 is the power of smooth peak value of emissive laser pulse, ρ is the reflectivity of the target, a0 is receiver aperture area, η 0 it is optical system transmitance, γ is atmosphere disappear smooth coefficient. This equation makes clear, as the addition that is apart from R, receive power to be reduced quickly. For logical choice parameter, r = 100 M, the amount that photon returns on the mobile area of detector is about hundreds of to thousands of, and the photon that blasts off normally exceeds 1012. These echo photon and setting photon are explored at the same time, and setting photon does not have any useful information. Use tape filter to be able to reduce the bias light compensation that arrives at detector, but cannot decrease 0, the influence of bias light compensation makes detect dynamic limits is reduced, noise (setting photon films noise) increase. Notable is, irradiation level of sun of face of typical condition go to the fields is less than 905 Nm in 1550 Nm place. Flight time (ToF) the fundamental signal of lidar is all round a car 360 ° × found a piece of complete 3D map to need to pass grating one bundle inside the area of 20 ° prismatic and junior line scanning, or many bundles stimulate beam of light to scan, again or beam of light whole Fu covers the limits of need collects the returned data that nod the cloud. Former the scanning that be called (Scanning) lidar, latter calls glitter (Flash) lidar. Scanning lidar has a few kinds of kind. The first kind of means, it is with Velodyne exemple (San Jose, CA) , lidar platform is installed in coping, this radar gives the pulse of laser of 64 905 Nm with the speed of 300 ~ 900 Rpm rotates and blasting off. The avalanche photoelectricity diode that every bundles of beam of light has a correspondence (APD) detector. More similar another method is to use rotating much face lens, the banking angle of every face is spent differ somewhat, thereby with what differ azimuthal reflex individual pulse beam of light with bevel angle guiding. The mechanical movement component in these two kinds of designs has exterior drive the breakdown risk when the environment is harsh. Bank the pine is new-style 100 meters of class drive automatically APD S14137 of silicon of lidar detector 16ch - 01CR the 2nd kind of more compact scanning lidar, its method is to use system of cable of personal computer of a miniature (MEMS) Zhen Jing, with planar direction electric guiding gives a bundle or many bundles of beam of light. Although go up to still have athletic part in the technology (oscillation lens) , but the scope of oscillation is very little, frequency is very tall also, enough prevents the mechanical resonance between car of MEMS Zhen Jinghe. However, geometrical dimension of Zhen Jing limitted its oscillation scope, this makes the perspective becomes finite -- a defect that this is MEMS method. However, this kind of method because cost is low, can come true degree tall and get the attention of people. Bank the Munich Shanghai bare gain this year meets product of loose newest MEMS Mirror 2018 in showpiece optical photograph controls array (OPA) technology, it is the 3rd kind of lidar technology that shares competition, it with reliable " fixed component " design and increasingly popular. It the array that by smooth illuminative of be concerned with optical antenna comprises is formed. Beam of light changes direction is when giving off light through controlling every unit independently phasic will come true with amplitude, be in interference to produce ideal illume way at far field thereby, implementation arrives from single light beam the change of much beam of light. Unfortunate is, smooth loss limitted the usable scope of all sorts of OPA component. Flashy lidar will be full of light in target setting, and the visual field photograph of illume area and detector matchs. Detector is the APDs array on explore photometry anxious plane. Every APD measures the ToF of feature of target of the image on its independently. This is a kind true " not mobile component " method, among them tangent direction (perpendicular, level) the limitation that resolution is resembled element dimension by 2 dimension detector. However, the main drawback of flashy lidar is echo photon amount: Once be apart from 10 meters more than several, the amount that returns light is too little, cannot undertake reliable exploration. If not be the form that direct consumed covers all exploration environments to use structural light however (choose lineup form for example) , and the tangent resolution with particular sacrifice, can heighten echo luminous intensity. In addition, perpendicular antrum face launchs laser (VCSELs) make go out in what different way shoots thousands of bundles of beam of light at the same time shoot become a possibility. Bank get the broadband that because electronics of weaker, exploration part designs its echo pulse,the contrast of smooth semiconductor detector that the pine can use at lidar casts off the limitative ToF lidar of ToF law is wider and easily the influence of noise, and threshold value sparks meet those who produce Δ T measure an error. Accordingly, frequency modulation is successive wave (FMCW) lidar is one kind very significant replace a method. In FMCW radar or chatter modulation radar, aerial emits frequency continuously by the radio wave of modulation. For example, as time T from? Do 0 linear increase? Max, next as T from? Is Max linear reduced to? 0. If the wave shift inside certain distance is reflexed on the object,wind emissive point, its instantaneous frequency differs the radio wave that emits with this instant. This one difference brings about by two elements: Reach its to the distance of the object relatively radial speed. Can get frequency difference through electronic measurement technique, the distance that calculates an object with chronometer and speed (see figure below) . In chatter radar, measure FB1 and FB2 through the electron, can determine rate of the distance with reflection target and its radial. Below the inspiration of chatter radar, FMCW lidar can be obtained through different kind. In the simplest design, people can chatter ground adjustment enlightens the light intensity of the target. The same rule that this frequency stands frequency of FMCW radar carrier wave (for example Doppler effect) influence, returned light is explored by smooth detector and restore modulation frequency, output is magnified and allow to measure frequency to move thereby with mixing of itself oscillation frequency, calculate from this the space that gives a cause and its speed. But FMCW lidar has certain limitation, compare with ToF lidar photograph, it needs more computational capability, because this is born,help sb to fulfill his wishes three-dimensional surround the rate when the graph is slower, and measure precision very sensitive to the degree of degree of linearity when the modulation when chatter. Although design a kind of function,perfect lidar system has challenge sex, but these challenges cannot be not overcome. As research continuity, we are more and more adjacent produce end hind at most car can the times of complete automation. Textual author United States bank loose research scientist: Slawomir Piatek United States bank loose sale engineer: Jake Li bibliographical reference 1. J. Wojtanowski Et Al. , opto - Electron. Rev. , 22, 3, 183 - 190 (2014) . CNC Milling CNC Machining