Lidar regards the core of numerous intelligence equipment as sensor, its application is already special and wide. We can drive in nobody nowadays means of forklift of robot of car, service, AGV, intelligence politics the figure that lidar sees again and again on traffic and automation product line, also the position that enough shows it is indispensable on catenary of artificial intelligence industry.

 

Current the mainstream lidar product on market, use at the environment to explore the radar that builds with map compose, can divide by technical course cardinal principle it is two kinds, one kind is TOF (Time Of Flight, time flight law) radar, another kind is radar of law of trigonometry range finding. These two nouns believe a lot of people are not new, but should say these two kinds of plan to who after all to cost, application from principle, function actor what bad, and what is the reason of backside, perhaps everybody is returned more or less somewhat interrogative. Small today make up with respect to cast a brick to attract jade-offer a few commonplace remarks by way of introduction so that others may come up with valuable opinions, do with respect to these problems analytic.

 

One, principle

 

Following plan institute show trigonometric principle, laser launchs laser, arrive in illuminate after the object, reflex is received by linear CCD, because laser and detector are removed,one paragraph is apart from, according to is so optical method, the object of different distance will become the position that resembles differring on CCD. Have consideration according to trigonometry formula, can push derive the distance of the object that be measured.

 

Light views a principle, feel quite simple.

 

Graph 1, principle of trigonometric range finding

 

However the principle of TOF is more simple. If the graph is shown 2 times, laser shoots pulse of a laser, leave ejaculation time by clock record, return light is received via receiver, record the time of next return by clock. Two time photograph decreases the ” of “ flight time that got light namely, and velocity of light is certain, because this is after foregone speed and time,can calculate very easily a distance.

 

Graph 2, principle of TOF range finding

 

Regrettablly is, like if all things are done,rising as wanting simple, that world is too good. These two kinds of plan can have respective challenge when specific implementation, but photograph comparing rises, the difficulty that TOF should capture wants to be gotten more apparently much.

 

The implementation difficulty of TOF radar basically depends on:

 

1.It is timing problem above all. In TOF plan, the distance measures those who rely on time. But velocity of light is too fast, because this wants to obtain accurate space, to timing systematic demand also becomes very high. A data is, lidar should measure the interval of 1cm, corresponding time span is 65ps about. The classmate that is familiar with electric character a little should know what this backside means to circuit system.

 

2.It is the processing of pulse signal next. The face distributes a share again here:

 

A) is laser: Be opposite in trigonometry radar laser drive hardly what requirement, because measure the place of dependent laser echo, need a successive light to go out only so it is OK to shoot. But TOF is no good however, not only swash wanting arteries and veins is smooth, and quality is returned cannot too poor, an arteries and veins ejaculation light of TOF radar is at present wide control in second of a few accept, ascendant edge is to ask to had been jumped over more quickly more, the laser drive plan that accordingly every family property tastes also is the branch that has on any account.

 

B) is receiver another. Generally speaking the time that echo hour is differentiated is pair of ascendant edges actually is differentiated, when be being handled to echo signal accordingly, must make sure signal does not want as far as possible lack fidelity. Additional, even if signal is done not have lack fidelity, because echo signal cannot be an ideal square wave, issue pair of different objects in same space accordingly measure what also can cause forward position is fluctuant. Mix to the white paper of same position for instance the measurement of black paper, the likelihood gets the two echo signal of following graphs, and time measures a system to must measure giving these two forward position is same hour (because the distance is same space) , this needs special processing.

 

Graph 3, the echo signal difference of different reflectivity

 

Divide this beyond, sink still is faced with processing of a confusion of voices of signal saturation, bottom to wait a problem a moment, can say difficulty is heavy.

 

2, function PK, know its like that knowable its the reason why?

 

Said so much, actually the angle from downstream user, caring your implementation to rise to be returned simply is difficult. The user cares most nothing more than at 2 o’clock: Function and price. Say performance first, if understand the National People’s Congress of this industry to know more, TOF radar going up from function is excel triangle radar. But particular system now what respect, what is the reason of backside?

 

1.Measure an interval

 

Come from the principle say, the interval that TOF radar can measure is farther. Actually, the situation of the distance is measured in a few requirements, for instance nobody drive car application, it is TOF radar almost. Trigonometry radar is measured not far, basically have the reason of a few respects: It is the limitation on the principle, actually careful observation pursues 1 not difficult discovery, the object interval that trigonometry radar measures is further, the positional difference on CCD is less, after Yu Zaichao of as a result passes a certain space, CCD cannot differentiate almost. 2 it is trigonometry radar does not have method to obtain taller letter a confusion of voices to compare in that way like TOF radar. TOF uses pulse laser sampling, and return the influence of visual field of can strict control with reducing ambient light. These are the premise conditions that Sunday run measures.

 

Of course, space accident does not represent absolutely stand or fall, this depends on specific use setting.

 

2.Sampling rate

 

When lidar describes an environment, of output is the image that nod the cloud. The dot cloud that every second can finish measures a number, it is sampling rate. In rotate speed particular case falls, the amount nodding the cloud that sampling rate decided each frame image and the horny resolution that nod the cloud. Horny resolution is higher, the amount that nod the cloud is more, criterion image is right of surroundings depict more meticulous.

 

the product that goes up with respect to market, the sampling rate of trigonometric radar is commonly under 20k, TOF radar can be accomplished taller (for example the TOF radar PAVO of astral second is highest and OK the sampling that achieves 100k is led) . Investigate its reason, TOF is finished measure a need a smooth pulse, analysis of real time time also can be answered very quickly. But the operation course that trigonometry radar needs is time-consuming longer.

 

Graph 4, to same position object, different sampling leads into resemble the effect

 

(A) : Small sampling leads the design that nod the cloud; (B) : Tall sampling rate orders cloud atlas model (PAVO)

 

3.Precision

 

Lidar is a range finding equipment substantially, measuring precision because of what this is apart from is without doubt core index. On this, trigonometric the precision below close quarters is very tall, but as the distance further and further, the precision that its measure is met worse and worse, because trigonometric measurement and angle are concerned,this is, and increase as the distance, surprise of differential seat angle will be less and less. The tagging that uses percentage often is when so trigonometry radar is tagging precision (be like commonly 1% ) , so the biggest when the distance of 20m error is in 20cm. And TOF radar is to count flight time, time measures precision not to increase as length have apparent change, because this is most,TOF radar is in a few meters measure a few can maintain inside limits centimeter precision.

 

4.Rotate speed (frame is led)

 

In mechanical radar, picture frame is led even if decide by the rotate speed of electric machinery. Current the 2 dimension on market lidar, the top rotate speed of trigonometry radar is normally under 20Hz, TOF radar can accomplish 30Hz-50Hz left and right sides. Normally trigonometry radar uses the structure that uses fluctuation fission normally, namely above the part that turn is in charge of laser blasting off, receive and collect, next parts are in charge of electric machinery drive and power supply waiting, overweight athletic package restricted higher rotate speed. And the structure of half solid state that TOF radar uses unifinication normally, electric machinery needs to drive illuminator only, the power comsumption of electric machinery is very accordingly small, and can support rotate speed is higher also.

 

Of course, the distinction of the rotate speed that mentions here is a of pair of existing products objective analysis only. Actually rotate speed and radar use TOF still is trigonometric the connection that does not have essence, the multi-line TOF radar of the mainstream also is the structure of adoption fluctuation fission, the optical design of coaxial after all structure gets a lot of limitation. The rotate speed of multi-line TOF radar also is commonly under 20Hz.

 

Nevertheless, high rotate speed (perhaps say tall frame is led) resembling the effect to nodding the cloud to become is very significant. Tall frame is led more the object that benefit moves at taking high speed, for instance the freeway goes up upgoing car. In addition, when oneself proposes a plan, the radar in motion builds a graph to be able to produce distortion (cite a case, if a dormant radar scanning circuit is a circle, so when radar moves point-blank, the picture that scanning gives becomes an ellipse) . Apparent, high rotate speed is OK the better effect that reduces this kind of distortion.

 

3, cost

 

If see function compare only, it seems that the function of TOF radar has pressed trigonometry radar completely. Nevertheless the competition of the product is not performance data merely than going all out, the user cares still the price, stability and service are waited a moment.

 

Be in at least cost respect, at present the cost of trigonometry radar is under TOF radar, the trigonometry radar cost of close quarters has been in 100 yuan of level. And the price that imports TOF radar at present is about at every turn 10 thousand yuan of above. Can say, high price is the main factor that application of limitative TOF lidar extends further.

 

Nevertheless, as in recent years the rise of manufacturer of domestic TOF radar, the cost of TOF radar has gotten considerably reduce, the price photograph of product of homebred TOF radar is compared at importing a brand, had had quite great competition ability. Future, perfect the farther promotion that measures with shipment as what manufacture technology, the cost that believes TOF radar still can be compressed further, fall to mix the level of trigonometry radar close also is not to be impossible.

 

4, apply setting

 

The setting of trigonometry radar basically is indoors the application of stone’s throw, the most typical setting sweeps the floor namely robot. And in monitoring area per fire detector bigger setting (for instance bazaar, airport or station) , and the setting outdoor, the application of TOF is more wide. What be worth to be carried additionally is, this plants trigonometry radar the plan of bare and outer roll, make its product is in dustproof and waterproof respect is very flimsy, in the application of a few special setting, the workshop classics regular meeting that for instance AVG Xiaoche works has a lot of dirt, below this kind of environment, the electric machinery of trigonometry radar damages very easily. Under photograph comparing, the half solid state that TOF radar uses is designed, can have more outstanding defend the effect, working life is longer also.

 

Graph 5, PAVO of lidar of astral second TOF

 

Current, domestic TOF radar is developing quickly, astral second (SIMINICS) the PAVO of 2D TOF lidar that roll out, can achieve 20m measure an interval, the rate nodding the cloud of 100kHz, the highest angle resolution of 0.036° , and of IP65 defend grade, its application has involved nobody to drive, robot, AGV, how to prevent, a lot of domain such as road politics, it is the outstanding delegate of homebred TOF radar.