Assembly of a Sensor - Übersicht€¦ · · 2013-07-31Properties of the Telemetric Signals ... A...

Bachelorarbeit : Assembly of a Sensor Alexis Ratouis PAM8

Betreuer: Herr Prof. Leibl

Assembly of a Sensor SS 2012

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Summary 1. Introduction ..................................................................................................................................... 4

1.1. The Topic : Assembly of a Sensor ............................................................................................ 4

1.2. Presentation of the Work ........................................................................................................ 5

2. Presentation of the different types of Rangefinder ........................................................................ 6

2.1. Rangefinder: What is it? .......................................................................................................... 6

2.2. The applications known for the Rangefinder .......................................................................... 7

2.3. Rangefinder naturally found in the Wild ................................................................................. 8

3. First Study: Laser Rangefinder ......................................................................................................... 8

3.1. Introduction ............................................................................................................................. 9

3.2. Overview ................................................................................................................................ 11

3.2.1. Definition of a sensor .................................................................................................... 11

3.2.2. Properties of a sensor.................................................................................................... 11

3.3. Properties of the Telemetric Signals ................................................................................. 13

3.3.1. Emitted Signal ................................................................................................................ 13

3.3.2. Received Signal .............................................................................................................. 13

3.3.3. Detection of Optical Signals .......................................................................................... 15

3.4. Accuracy of Measurements ............................................................................................... 15

3.4.1. Systematic Errors ........................................................................................................... 16

3.4.1.1. Geometric .................................................................................................................. 16

3.4.1.2. Size of the beam on the target and slope of the target ............................................ 16

3.4.2. Random Errors ............................................................................................................... 17

3.4.2.1. Error due to the Atmospheric Turbulence ................................................................ 17

3.4.2.2. Error related to Signal to Noise Ratio (SNR) .............................................................. 17

3.5. Reach of Rangefinders ....................................................................................................... 19

3.5.1. Target Detection ............................................................................................................ 20

3.5.2. Reach ............................................................................................................................. 23

3.6. Systems using a Coherent Detection ................................................................................. 24

3.6.1. Impulsive telemetry with Coherent Detection .............................................................. 24

3.6.2. Frequency Modulated Continuous Wave (FMCW) ....................................................... 26

3.7. Systems using a Direct Detection .......................................................................................... 28

3.7.1. Telemetry by Phase Comparison ....................................................................................... 29

3.7.2. Telemetry modulation type “Chirp” .................................................................................. 30


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3.7.3. Time of Flight Telemetry ................................................................................................... 31

3.8. Triangulation ......................................................................................................................... 33

3.9. Conclusion ............................................................................................................................. 35

4. Market of the Laser Rangefinder................................................................................................... 36

4.1. Keyence Corporation ............................................................................................................. 36

4.1.1. LK Series Laser Displacement Sensor ............................................................................ 37

4.1.2. LJ-Series: 2D Laser Displacement Sensor ...................................................................... 40

4.2. Sensor Instruments GmbH .................................................................................................... 42

5. Market of the Ultrasonic and Infrared Sensor .............................................................................. 43

5.1. Ultrasonic Sensor ....................................................................................................................... 43

5.2. Infrared Sensor .......................................................................................................................... 47

6. Conclusion ..................................................................................................................................... 51

7. Sources .......................................................................................................................................... 52


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1. Introduction

1.1. The Topic : Assembly of a Sensor

In a confined space, there is an object (red in the figure 1.1) and we are trying to

identify it. So the goal of this experiment is to find a sensor, which will give us the position of

the object and its form. This sensor must see in all three direction (x,y,z), to see all the

possibilities.

The sensor is placed on a block (a robot’s arm (blue in the figure 1.1)). This robot’s

arm can move in all three directions (x,y,z) with a range maximal of 200 mm. and the

distance between the sensor and the object can vary from 10 to 200 mm.

To remember:

The sensor is on the block

There is 10-200 mm between the sensor and the object to identify

The robot’s arm have a liberty of 200 mm in all three directions

We want one sensor (and if possible not too costly)

Robot’s arm

which will move

in all three

directions Confined Space

Object to

identify

Figure 1.1: Diagram summarizing the tropic dealt with


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1.2. Presentation of the Work

After a quick introduction of the different sensors, that we will call rangefinders too,

and their application in our world of today, we will concentrate ourselves on the laser

rangefinder, how is it composed, how it works, the different type of laser rangefinder, the

limits and the advantages of this type of rangefinder.

We are a little evading the two other type of sensor because after some research, we

have seen that the most interesting is the laser rangefinder.

But we will nonetheless present some product of the two other type of rangefinder

to compare the proprieties of the three sorts of rangefinder.

We will conclude on our choice of rangefinder.


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2. Presentation of the different types of Rangefinder

2.1. Rangefinder: What is it?

A laser or optical rangefinder, also called EDM (for Electronic Distance

Measurement), is a device for measuring distance using a light beam (laser or infrared) or

ultrasound to calculate distances.

The main advantages compared with conventional measuring instruments (tape

measure, surveyor's chain ...) are speed and accuracy. Moreover the rangefinder

automatically calculates area and volume by multiplying two or three successive

measurements.

Today many techniques allow this, using different areas of electronics. The different

types of rangefinders are these below:

- Laser Rangefinder: as its name suggests, it uses a laser beam to realize the measurement. A

laser beam is projected onto a target which in turn refers to the beam. The ECU (Electronic

Control Unit) calculates the phase difference between the transmission and the reception.

The distance between the user and the target is calculated. This technology has many

advantages: reduced weight and size, speed and precision, low cost. The vast majority of

rangefinders are of this type, both for the public and professionals alike.

- Ultrasonic Rangefinder: An ultrasonic telemeter is used to measure distance. The principle,

inspired by the bat, is to send a burst of ultrasound to the reflecting object, such as a wall or

a window, and capture the echo returned by this object. We have access to the distance

between the rangefinder and the object by measuring the time it takes for the echo to

return to the rangefinder. Knowing the speed of sound, we deduce the distance sought. The

advantages of using such a measure are many. The measurement is fast even several

meters, and we can safely measure distances difficult to access. These models are much

cheaper but they are not very accurate, especially over long distances, because the sound

waves are very sensitive to the environment, for example: furniture may be sufficient to

interfere with the measurement of a room.

- Infrared Rangefinder: these devices require reflectors, the timing is difficult to implement,

and these models tend to be used in a fixed installation, like in the construction industry to

monitor a work of art.


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Be careful not to confuse "laser range finder" and "ultrasonic rangefinder with laser

pointer": on this type of device the laser is only used to facilitate scoring and is not used for

the calculation of the length, precision is no better than a conventional ultrasonic

rangefinder.

2.2. The applications known for the Rangefinder

There are currently different types of application for rangefinders. You can find

models in sales in both the public than the private sector. Here are some examples of these

applications for the laser Rangefinder:

- Speed control:

This principle is used by law enforcement to conduct speed checks. The radar

implements pulse trains of infrared radiation emitted by a laser. When the beam encounters

a moving target (vehicle), a fraction of the beam is reflected back to the radar (reflected

beam). The measurement of the targeted vehicles speed is determined from the variation of

the interval between the pulses reflected by the vehicle. Over the vehicle moves away

quickly, the time between two successive reflected pulses increases (Doppler Effect).

- In the navy:

It is used in the Navy for civilian applications (pollsters for the depth of water below

the keel of a ship submerged or immersed) but also military to calculate the distance

between the sender and the intended air, land, immersed or submerged.

- In the army:

Technology has enabled the development of support systems for fire control with the

development of laser rangefinder coupled to a ballistic computer whose purpose is to

calculate the correction to be applied to the angle and orientation of the barrel in function of

distance, speed and direction of the goal, the type of ammunition in the cylinder head since

this gun can fire various types of shells, the speed and direction of the tank shooter, speed

and wind direction etc…

Rangefinders provide an exact distance to targets located beyond the distance of

point-blank shooting to snipers and artillery. They can also be used for military reconciliation

and engineering.

Handheld military rangefinders operate at ranges of 2 km up to 25 km and are

combined with binoculars or monocular. Some rangefinders have cable or wireless

interfaces to enable them to transfer their measurement data to other equipment like fire

control computers.


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- Sports:

Laser rangefinders may be effectively used in various sports that require precision

distance measurement, such as golf, hunting, and archery.

For example, Golf: rangefinders appear more and more in the bags of pros and

amateurs. Laser rangefinders are like binoculars. We aim for the target. A laser beam is sent

and comes back. The elapsed time is recorded and translated into distance. Some models

are more powerful than others and the most sophisticated capture the reflectors that some

clubs put on their flags. Some even consider the slope to calculate the distance. They can be

used on all routes, and most importantly, you can aim the flags for a specified distance

approach shots.

- In our cars:

In almost all new model of cars we can find rangefinders which helps in the

measurement around the car when we want to park it.

2.3. Rangefinder naturally found in the Wild

There is a lot of different species who use rangefinder to lead themselves or to locate

something else. For example dauphins and bats, these two animals use ultrasonic

rangefinder to hunt or to locate themselves. Their capability to use this sonar is way better

that everything that we can find in the commerce.

We will now begin to study the different sort of rangefinders to find the one that is

the most suitable for our need.

3. First Study: Laser Rangefinder

We will first study this kind of rangefinder because it is the most common and the

one that present the most different type of application, so we will first decide between all

these find the one that correspond at our experiment.

A laser rangefinder is an active system of remote detection, in the same way as the

radar, with the peculiarity to allow the measure a distance with a strong spatial resolution.

The radar uses an electromagnetic radiation of wavelength λ of the order of cm. The minimal

difference which can be obtained at the release of a transmitter is limited by the diffraction

in λ / D where D is the diameter of the antenna. The use of the optical waves, the

http://en.wikipedia.org/wiki/Golf

http://en.wikipedia.org/wiki/Hunting

http://en.wikipedia.org/wiki/Archery


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wavelength λ is of the order of µm, allows to reduce the difference of the beam for a surface

of emission given by a report going from 104 to 105.

It allows locating exactly the measure.

The first fields of application of rangefinders were originally military and scientific,

one of the first applications consisted in measuring the distance separating our planet and

the moon. The development of laser sources with semiconductors, more collectively known

under the name of diodes laser, widely contributed, thanks to their low cost, their wide

distribution, their small size, their ease of use, in the development of the devices of

telemetry for the industrial and civil application areas. For example, the use of a rangefinder

arranged in front of an automobile was envisaged as system anti-collision: the rangefinder

detects any object being on the trajectory of the vehicle and estimates its distance, this

information can then be transmitted to the driver. A rangefinder, installed on the deck of a

boat, can be used as assistance in the coastal or river navigation. Numerous applications, in

the field of transport, where the evaluation of the distances is important, can be again

imagined. In the field of the geology and of the topography, a tool as the rangefinder laser

facilitates the statements of the ground. The recreational activities are also concerned,

indeed certain sporting brands propose to their customers, hunters or golfers, mobile laser

rangefinders to help them in the practice of their activity.

The aimed application, for which we are doing this work, is the imaging in three

dimensions. We search that in a closed space, the rangefinder, installed on an automated

arm, can move around an object at a certain distance of this one, the purpose being to

identify the shape of the object.

3.1. Introduction

All the systems of remote detection using a laser are generally grouped under the

English acronyms lidar, which means Light Detection and Ranging, or ladar, which means

Laser Detection and Ranging. Under these names hides in reality a multitude of techniques

and systems. It is for example possible to analyze the fine spatial structure of the

atmosphere, to measure fields of concentrations of chemical species in domains as the

measure of rate of pollution or the study of serious accidents in the nuclear domain. We

shall limit ourselves in this part to the systems of remote detection which has for objective

to realize a measure of distance: rangefinders. All these systems can be split into two

families using each a different principle of detection: the coherent detection (figure 3-1) and

the direct detection (figure 3-2).


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It exists, generally, in all the systems of telemetry, a block of emission containing a

modulated laser source and optics of shaping of the beam, a block of reception constituted

by a photo-detector and by optics of reception, and finally, a block dedicated to the

processing adapted to the signals, which delivers the information of distance. In the case of

the coherent detection the power and the phase of the bright wave intervene in the

mechanism of the detection, a part of the emitted signal is taken and directly sent on the

photo-detector and comes to mix with the signal from the object.

Lo

cal

osc

illa

tor

Target

Laser Beam

Light scattered from the Target

Modulated

laser source

Detector

EMISSION BLOCK

RECEIVING BLOCK

PR

OC

ES

SIN

G B

LO

CK

Sig

nal

pro

cess

ing

Figure 3.1: Plan of a rangefinder with coherent detection

Target

Laser Beam


Modulated

laser source

Detector

EMISSION BLOCK

RECEIVING BLOCK

PR

OC

ES

SIN

G B

LO

CK

Sig

nal

pro

cess

ing

Figure 3.2: Plan of a rangefinder with direct detection


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In both architectures, the signal of modulation of the laser allows to code the

intensity, the frequency or the phase of the light wave. This coding and the processing of the

signal determine the performances of the system in term of precision and pace. The reach is

limited by the signal on noise ratio of the reception block.

3.2. Overview

A rangefinder laser is thus constituted by various parts which can be considered

independently one from the others or, on the contrary, in a global way. The approach under

the shape of a complete system means presenting a rangefinder as an intelligent sensor of

distance who supplies information of distance after an electro-optical excitement.

Consequently, by considering first of all the rangefinder as system, we begin our

presentation with some definitions relative to the sensors whom we shall need afterward.

3.2.1. Definition of a sensor

A sensor is a system which transforms a stimulus, a priori of any physical nature, into

an electric signal, image of the answer to the stimulus. We limit our definition to the sensors

delivering an amplitude of electric output, which is the case the most common nowadays.

The electric signal can be afterward characterized by its amplitude, its frequency, its spectral

density, its phase, its energy or its power.

3.2.2. Properties of a sensor

Characteristic sizes common to all the types of sensors were defined to be able to

compare their performances more easily.

Mechanical, magnetic,

optical, chemical

excitement

Characteristic electric

signal of the sensor

SENSOR

Response: Stimulus:

Figure 3.3: Sensor


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Precision: the precision is represented by the difference between the real release of the

sensor and the ideal value of this release. The more this gap is weak, the more the precision

is better. The term of error is also used to quantify the precision through the digital

evaluation of the difference. The errors can have diverse origins, either they are bound to

the sensor, or they depend on the environment. They can be separated in the following way:

Systematic error: the error takes an identical value for a given cause, it is, a priori, the error

due to a reproducible defect of the system or the sensor, and consequently, she can be

corrected during a calibration.

Random error (in the mathematical sense): her influence can be reduced by increasing the

number of measures. Indeed, the uncertainty on the measure is translated by the probability

that the size of the output, for example the distance z, is included between z - and z +

within 95 %. If the probability distribution is normal, with a standard deviation of , then =

2.

Error bound to the environment: she translates the influence of outer parameters such as the

temperature, the degree of hygrometry, the presence of electromagnetic field... It is

sometimes necessary to protect the sensor against these types of influence.

In every case, it is necessary to take into account all the sources of errors to know the

precision of the system.

Resolution: the resolution is determined by the smallest increment of the stimulus which

can be detected in output. It is in fact about the capacity of distinguishing two very close

values of stimulus.

Sensibility: the sensibility characterizes the capacity to supply a strong variation of the size

of exit S for a low variation of the size of entry E. She is represented by a coefficient of

sensibility given by the slope dS / dE.

Area of measure: the area of measure is the difference between the extreme values that the

sensor can supply.

Linearity: the linearity characterizes the quality of the measure for a sensor giving as size of

the exit a linear function of the entry.

Reproducibility: the reproducibility translates the capacity to reproduce an output given for

a given entry, in the same conditions of measure. In case the results stemming from

measures are scattered, it is possible to define a repeatability error of the sensor.


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3.3. Properties of the Telemetric Signals

We present here the telemetric signals from which the measure of distance is

possible.

3.3.1. Emitted Signal

As we saw it previously, in telemetry, the signal of modulation applied to the laser

allows to code the intensity, the frequency or the phase of the emitted electromagnetic

wave. In the case of radars, the frequency of this electromagnetic wave, called a carrier, is of

the order of some kHz to several GHz. The carrier frequency in the visible and close infrared

is of the order of some hundreds THz. We are going to be interested in the electric field of

this electromagnetic emitted wave, noted in the complex plan:

( ) ( )

3.3.2. Received Signal

Let us suppose a punctual target, situated at the distance z0 of the origin of time and

animated by a constant radial speed v, positive in merger. The target backscatter a part of

the energy emitted with the signal E(t). The signal received at the instant t is equal to the

emitted signal, allocated by a coefficient of mitigation and delayed by :

( ) √ ( )

The distance between the rangefinder and the target is then:

( )

The signal received at the moment t was emitted at the instant t - and was thus reflected

by the object at the instant

. Consequently, the distance traveled on the return route is

given by:

(

) (

)

And so comes:


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With:

and

Finally:

( ) √ (( ) ) [ (( ) )]

The received signal is a sinusoidal signal with the frequency ( ) modulated by the

envelope signal a. The radial movement of the target causes a modification of the time scale

which is multiplied by ( ). Considering speeds involved, the modification of the time

scale is insignificant and:

(( ) ) ( )

As v << c, the distance of the target is translated by a simple delay between the received

signal and the emitted signal:

The modification of the time scale moves the emission frequency of a quantity called

Doppler frequency. As v << c it comes:

Where the wavelength of emission is:

The signal of reception has thus the shape:

( ) √ ( ) ( )

Time of flight (distance):

Doppler Frequency (speed):

In telemetry, it is the time of flight that is generally exploited for the measure of

distance. The phase difference is used in interferometry to measure movements and

finally the measure of the Doppler gap allows to determine the speed of movement of the

target.


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3.3.3. Detection of Optical Signals

Photoelectric effect is the mechanism the most used to detect the optical signals.

This effect is not immediate but possesses a characteristic time of the order of 1 ns in

semi-conductors. The probability of absorption of a photon by an electron is proportional to

the square of the integrated field at the characteristic time .

The intensity of the electric current delivered by the detector is thus proportional to

the square of the field and is, in the case of the optical signal studied previously:

( )

∫ ( ) ( )

Where is the sensibility of the detector. This expression allows determining the speed of

the photoelectric current. In the case of a coherent detection, it is possible to detect the

module and the argument of the complex shell ( ). When the detection is direct, the

information of phase is lost because the response of the receiver is quadratic and slow

compared with the optical frequency. We are now going to be interested in the fundamental

limits of a system of telemetry laser in term of precision and reach.

3.4. Accuracy of Measurements

In telemetry the precision of a measure is mainly bound to two uncertainties. The

first one, noted , is systematic and attributable to instruments and methods of measure

and thus dependent of the system. For example, if the measured size is a distance z with a

systematic error , then the real value of the distance is given by . Furthermore, if

several systematic errors come to overlap, we just have to add their value and taking into

account their sign. The second, noted , is random, if we consider n independent

effects generating it comes:

√∑

In the next two paragraphs, we are going to mention the main sources of systematic and

random errors occurring in the telemetric systems.


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3.4.1. Systematic Errors

3.4.1.1. Geometric

We saw in the introduction of this part that the telemetric systems consisted of

emission and reception module. If the distance between the axes of both modules is noted e

and the distance between the rangefinder and the target is noted z, then the measured

distance is:

( √ )

Generally this systematic error is neglected for important distances: e << z. For example, for

a target at 50 m and one enters axis of 10 cm, the moderate distance is overestimated of

100 µm.

3.4.1.2. Size of the beam on the target and slope of the target

Until now, we supposed that the beam was punctual. In practice, in the case of any

target, this hypothesis is rarely verified. The surface of the target can be tilted compared

with the beam or still irregular with discontinuities. This reality leads to more or less

important distortions on the signals. The more the spot on the target will be important, the

more the signals will be subject to these distortions. These effects can introduce, according

to the method of processing used, an additional error.

For example in the case of a time of flight rangefinder, the incidence of the beam on

an inclined plan will have the effect of widening the impulses. The use of a threshold

detection on the front of the ascent of the impulse will thus result of underestimating the

measured distance.

The dimensions of the laser spot on the target thus limit the sense of the word

"precision" to those. Furthermore, contrary to the geometrical error which is perfectly

known, this error is dependent on characteristics of the target a priori unknowns and is not

thus compensable. It is necessary to add that this error is much less important than for

radars, laser beam having a much upper power of localization of the measure. For example,

for a beam with a divergence of 0,1 mrad, the laser spot on a target at 50 m has a diameter

of 5 mm: the precision is limited to that value.


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3.4.2. Random Errors

3.4.2.1. Error due to the Atmospheric Turbulence

As we saw it previously, the formula

is used to determine the distance of the

rangefinder to the target according to the time of flight and the speed of light. This formula

was written in the hypothesis where the middle crossed by the laser beam is the space. But

the index of the air is not perfectly equal to 1 and can also vary along the optical path: the

value of the index of refraction n is dependent on conditions of temperature and on

pressure which vary locally in the atmosphere. The formula

spells then:

Where represents the average index along the optical route. The maximal

variance of the index is given by:

⁄

Where is the coefficient of structure of the index and the superior scale of the

turbulence, that to say the distance between the target and the rangefinder. Let us take an

example where the turbulence is maximal: . A distant target of 1 km will

introduce a standard deviation on the index of which in turn will introduce a 1 mm

standard deviation on the measure of distance z. A 50 m, the standard deviation on the

index is , on the distance it is about 20 µm.

3.4.2.2. Error related to Signal to Noise Ratio (SNR)

By taking for hypothesis of detection the filtering adapted in the presence of white

noise, Woodward showed that the average quadratic error (standard deviation) on the time

of flight , bound to the background noise which overlaps the signal, is given by the

relation:

√

And so is given the average quadratic error (standard deviation) on the measure of distance:

√


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Where SNR is the signal on noise ratio of the electric powers of the detection. The

parameter Ф is the spectral range:

∫ | [ ( )]|

∫ | [ ( )]|

By using the previous formalism, the average quadratic error on the measure of the Doppler

frequency is:

√

And so is given the average quadratic error (standard deviation) on the measure of speed:

√

Where Θ is the temporal range:

∫ | ( )|

∫ | ( )|

The principle of radar uncertainty is expressed by the relation:

This inequality is obtained by making the product of the relations

∫ | [ ( )]|

∫ | [ ( )]|

and ∫ | ( )|

∫ | ( )|

and by using the inequality of Cauchy-

Schwarz. The formula

can be used to quantify the average quadratic error on the

measure of a time or of a frequency. Indeed, the product expresses itself, considering

the principle of radar uncertainty, by the inequality:

This relation shows that it is possible to reduce simultaneously the average quadratic

error of a temporal measure (measure of the time of flight) and the average quadratic error

of a frequential measure (measure of the Doppler frequency) by maximizing the signal on

noise ratio or the product : a high product can be obtained, for example, by using

an impulse having a wide spectre and an important duration (typically an impulse of

Gaussian shell linearly modulated in frequency).


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Here is in the case of an Gaussian impulse not modulated in frequency, used

generally in time of flight laser telemetry and in impulsive telemetry with coherent

detection, with the shape:

( ) (

)

Values of Φ and Θ:

and

So come:

√ and

√

As we saw it previously in the paragraph of the detection of optical signal (3.3.3), in

the case of a direct detection the information of phase is lost, the access to the measure of

the Doppler frequency, the speed, is impossible. In the case of a coherent detection the

obtaining of a weak average quadratic error on the measure of time of flight is made to the

detriment of the standard deviation on the measure of the Doppler frequency: for example,

for an impulse of half width at and a signal on noise ratio of 50, the standard

deviation on the measure of distance is about 2 cm while the standard deviation on the

measure of speed is about 240 m/s. Time of flight rangefinders using short impulses (ns) are

thus for direct detection and do not supply measure of immediate speed, however by means

of several measures of distances it is possible to them to estimate the speed of the target.

We introduced into this paragraph diverse sources of errors. Generally only the

random error due to the signal on noise ratio, dominating, is considered. However in case

we wish to make measures with a very big precision, the other errors are has to be taken

into account.

3.5. Reach of Rangefinders

The main purpose of radars is to determine first of all the absence or the presence of

a target, then secondly to estimate its position. In this paragraph we shall be interested first

of all in the first one of these objectives: the detection of a target. Indeed, as we shall see it

farther, the received signal is disrupted by a noise which has for origin the sensor itself and

its environment. This disturbance added to the signal can lead to an erroneous measure or a


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non-measure. It is advisable to choose a threshold detection such as the probability of

erroneous measure or non-measure is minimized.

We shall see that the value of this threshold participates in the determination of one

important characteristic of rangefinders: the reach.

3.5.1. Target Detection

The problem of detection is a problem of statistical decision: from an experiment (the

reception), the rangefinder has to make a decision concerning the presence or the absence

of a target. To solve this problem we develop a criterion of decision which determines the

membership in one or another of the hypotheses. The considered observation is:

Where s represents the useful signal and b the noise. Two hypotheses must be then

envisaged:

H0 : The target is not present

H1 : The target is present

The functions of density of probability of the random variables x and b, relative to the

hypotheses described above, are given by:

( ⁄ ) ( ⁄ )

( ⁄ ) ( ⁄ )

When the photo electric noise is dominant, its function of density of probability follows a

law of Poisson. In other cases, more frequent, where the various sources of noise are of the

same order, the central limit theorem can be invoked, the function of density of probability

of the noise is then considered as normal (Gaussian):

( )

√

We introduce the relation of credibility defined in the following way:

( ) ( )⁄

( )⁄

( )⁄

( ⁄ )

( )


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The test used to determine the threshold y0 of decision is:

Selection of the hypothesis H1 if: ( )

With ( ). The selection criterion for H1, by taking the logarithm of each of the

members of

√ , finally is:

Selection of the hypothesis H1 if:

[ ]

It is now a question of choosing a value for . To do this, we have at our disposition several

criteria defined in the works of the theory of the detection. We are quickly going to

introduce three most used criteria and we shall settle on one of them.

Criterion of the Maximum of Credibility

Here, the test concerns only on the comparison of the functions of density of probability

( ⁄ ) and ( ⁄ ), is to choose :

Selection of the hypothesis H1 if: ( ⁄ ) ( ⁄ ), that to say

Criterion of Bayes

The optimal choice, from the point of view of the maximization of the probability of correct

decision, knowing ( ) and ( ), is to fix the threshold in the following way:

( )

( )

By choosing, for example , we obtain:


[ ]

As the probability of H0 is twice superior to that of H1, the criterion of Bayes requires a value

of y superior for the selection of H0 compared with the criterion of the maximum of

credibility for which this information is not used. In this case, the criterion of Bayes gives

naturally a better rule of decision. However and generally ( ) and ( ) are a priori not

known, which makes this criterion difficult to apply.


22

Alexis Ratouis PAM8

Criterion of Neyman-Pearson

Both criteria quoted previously are hard to assess. The approach Neyman-Pearson, as for

her, brings to a rule of decision subject to a quantitative evaluation. Indeed, until then, no

constraint was applied to the criteria. We now introduce the probability of false alarm: H1 is

selected while H0 is true:

∫ ( ⁄ )

∫ ( ⁄ )

And the probability of detection:

∫ ( ⁄ )

∫ ( ⁄ )

Let us apply to the criterion the following constraint: for example , the rate of

false alarm tolerated is 1 %. The threshold is then calculated for:

∫

√ ( )

[ (

√ )]

The equation

√ which established the condition of threshold on ( ) is

transformed into term of observation on y by:


A digital resolution of

gives . The probability of detection is then given

by:

∫

√ ( )

[ (

√ )]

Thus with :

[ (

√ )]

We notice that depends only on the signal on noise ratio through √ ⁄ , and of course

of the value of chosen which determines in this example the parameter 1,646. The

function erf(x) aims towards 1 when x aims towards the infinity, which means that for a

signal on noise ratio, what is equal to ⁄ , important enough, the probability of detection

is close to the unit.


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Alexis Ratouis PAM8

Our choice will thus turn to the criterion of Neyman-Pearson which the rule of

decision is subject to a quantitative evaluation. For example, during the realization of a

rangefinder, the constraint on the rate of false alarm maximum tolerated will allow to fix the

threshold of detection and also to know the probability of detection for a signal on noise

ratio given. We shall see in the next paragraph that the reach of the system of telemetry

depends on the choice of the threshold of detection.

3.5.2. Reach

We saw previously that the signal on noise ratio plays a role determining in the

performances in terms of precision and in terms of detection of rangefinders.

The theoretical reach of a telemetric system is reckoned from the signal on noise

ratio noted SNR(z), because the return signal generally depends on the distance z of the

target. If SNR0 is the threshold that we settled beforehand:

( )

The maximal reach zMAX is determined by solving an equation of the type:

( )

Bayes threshold

𝑠

𝜎 ln

𝑠

Maximum of Credibility threshold

s / 2

Neyman-Pearson

threshold for 𝑃𝑓𝑎 SNR in the threshold

Figure 3.4: Illustration of the various thresholds of decision and probability of

false alarm according to the SNR in the threshold


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Alexis Ratouis PAM8

Until now our approach was rather general and did not depend in particular on

parameters of elements and on the environment of the rangefinder. Yet a preliminary

knowledge of all the parameters of the system is necessary to realize the calculation of the

signal on noise ratio.

Indeed, most of the noises depend on elements and on the environment of the

rangefinder. It is the case for example of the ambient noise caused by the sun rays, the

fluctuations in the signals due to the atmospheric turbulence and to the granularity laser, or

the noise generated by the photodetector and the electronic amplifier. The evaluation of the

signal on noise ratio is inevitably made for given architecture.

3.6. Systems using a Coherent Detection

The advantage of this technique compared with the classic interferometry is the use

of strong light impulses combined in a sensibility elevated in coherent detection. We are

going to be interested in this paragraph in the techniques of telemetry laser, adapted by

radars techniques, using a coherent detection.

3.6.1. Impulsive telemetry with Coherent Detection

Originally a single continuous laser was used. A part of the beam served as local

oscillator, the other part was sent towards an optical amplifier working during an interval of

time reduced to a frequency of recurrence given to produce the impulses. However, the

width of the obtained impulses was of the order of 10 µs and did not allow obtaining a

resolution in satisfactory distance.

To reduce the duration of the impulse and the complexity of the emission block due

to the optical amplifier, the use of a triggered laser, with impulses of width lower than a

micro second, was envisaged. This impulsive laser source is, furthermore, of strong power

(impulsion is of several mJ even about ten of mJ). The various triggered lasers used in the

systems of telemetry are the CO2 laser and more recently, with the development of the solid

lasers, the Nd: YAG and the Tm, Ho: YAG. Nevertheless, this laser of power must be

stabilized in optical frequency, which involves generally the use of the second continuous

"master" laser with a narrow and stable spectrum, in order to relay it to the "slave" laser of

power by injection. This second laser, at the same time, is also used as local oscillator. The

use of couplers with optical fiber allows to free itself from boring but necessary alignments

in the interferometric arrangements.


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Alexis Ratouis PAM8

As we saw it in the paragraph on the accuracy of the rangefinder, it is necessary to

make a compromise between the measure of distance and the measure of speed: the

resolution in distance is directly proportional to the duration of the impulse, whereas the

resolution in speed is conversely proportional in this period.

A means to free itself from this constraint is to modulate in amplitude the emitted

impulse, this technique is derived from the "compression of impulse" and from the

telemetric comparison of phase, which we shall detail afterward, she allows to obtain

simultaneously and exactly the information of speed and distance. Masters et al. use an

injected laser at 2,09 µm (eye safety), a part of the beam of the laser "master" is moved in

frequency by an acoustooptic modulator and is used to inject a triggered laser "slave" more

powerful to pass on to it its thiner spectral properties: the emitted impulse has a width of

500 ns and is moved by 27 MHz compared with the laser "master". The impulse emitted by

the laser "slave" is then sinusoidaly modulated by an electrooptical crystal:

( ) ( ) [ ( )]

( ) is the amplitude function, ( ) is the phase function and is the carrier pulse, the

other part is used as a local oscillator for the interferential mix with the backscattered

impulse by a target. The improvement announced on the resolution in distance, with regard

to a rangefinder with comparison of phase, is of a factor 70.

Target

Laser Beam

Light scattered from the Target Detector

EMISSION BLOCK

RECEIVING BLOCK

Loca

l osc

illa

tor

Stable

continuous laser

Triggered laser

Figure 3.5: Impulsive rangefinder with coherent detection


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Alexis Ratouis PAM8

The dimensions, the complexity, the cost of the impulsive rangefinders with coherent

detection limit their scope in the measures atmospheric as the measure of the wind speed

where of the height of clouds for example.

3.6.2. Frequency Modulated Continuous Wave (FMCW)

The modulation of the optical frequency used in telemetry FMCW is described

schematically on the figure 3.6. A scanning of frequency in the shape of double banister is

implemented to realize a measure of the Doppler effect. The fundamental difference with

the impulsive telemetry with coherent detection comes from the fact that the information of

distance is obtained in the frequential domain. The principle of the telemetry FMCW consists

in making interfere the reception signal with a part of the emitted signal and measure the

resultant beatings. If the object is in movement, the frequencies of beating obtained by

interference of the reference wave and the wave signal, spell:

{

The measure of the frequencies f1 and f2 allows to determine the distance z and the

speed v of the object as far as these two quantities do not vary in a significant way during

the time of the measure. The obtaining of v and z is immediate from the previous relations

Figure 3.6: Example of Modulation used in Telemetry FMCW


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Alexis Ratouis PAM8

which form a system of two equations with two unknowns. The advantage of this technique

is to obtain a resolution in distance lower than the mm.

The first lidars using a scanning of the wavelength were realized with CO2 lasers

emitting in 10,6 µm. At this wavelength, the problems of alignment and the fluctuations are

less critical than in the close infrared. However the systems with CO2 laser are generally

complex and cumbersome for applications requiring a moderate cost of manufacturing as

well as reduced dimensions.

Devices using diodes lasers and their dynamic properties of accordability in

wavelength were proposed to operate the technique FMCW. To solve the very critical

problems of alignment and coherence in the close infrared, diverse solutions were proposed.

The most original relaying on the use of the laser as emitter and receptor: the figure 3-7

describes a montage using a diode laser. By adding at the courant of polarization a periodical

courant in the shape of double banister, it is possible to modulate the frequency of the

emission of the laser. However, the major inconvenience of the use of a diode laser results

from jumps of modes and from the degradation of the temporal coherence of the oscillation

laser when the target sends back too much light in the cavity.

Target

Laser Beam


Detector

EMISSION-RECEPTION BLOCK

Laser diode or

modulated micro

laser

Processing

Variable attenuator

Figure 3.7: Rangefinder with linear modulation of the optical frequency using a

diode laser or a microlaser


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Alexis Ratouis PAM8

The development of miniature solid lasers (micro lasers) scanned in frequency by the

modulation of a electrooptical crystal placed inside the cavity laser allowed to free itself

from problems bound to diodes laser. The first rangefinder using this source laser (see figure

3-8) was realized in Léti. Measures of distance on a beach going from 1 to 10 m were

realized with a 1 mm reproducibility over a short period of acquisition. Indeed, the light

instability of the long-term micro lasers leads to a drift on the measure of the order of

several mm. The cadence or frequency of the measures is of 10 kHz, that to say, a measure

all 0,1 ms.

3.7. Systems using a Direct Detection

Goldstein, in 1963, suggests using the peculiarity of lasers to produce in an interval of

very short time an intense impulse of light associated with a direct detection with the aim of

measuring important distances. The first anticipated applications consisted in measuring the

distance between the earth and the moon or the measure of the distance to a vehicle. In

1968, Goldstein presents the first rangefinder with direct detection using a laser with semi-

conductor with a reach of 200 m on a natural target. The main advantage, compared with

the systems possessing a coherent detection, is the simplicity of implementation: indeed,

the alignments are less critical, the elements are less numerous, the dimensions of the

rangefinder are reduced so that he can be "portable". These are the reasons which,

afterward, favored the development of rangefinders with direct detection and led to

commercial devices. In this paragraph, we shall describe the main systems using this type of

detection.

Figure 3.8: Rangefinder using a micro laser scanned in frequency developed in

Léti


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Alexis Ratouis PAM8

3.7.1. Telemetry by Phase Comparison

The bright power stemming from the source laser is modulated according to a law of

the type:

( ) [ ( )]

P0 is the average power, m the factor of modulation included between 0 and 1 and fm the

modulation frequency. This wave is emitted towards the target situated at the distance z. A

weak part of the power backscattered by the target is received by a detector with an equal

delay in the time of flight . The detected power is thus of the shape:

( ) [ (

)]

The electric signal stemming from the detector is a sinusoidal signal of the same frequency

fm as the command, but disorientated of a quantity ⁄ . The signal processing

allows to determine directly the phase and thus to calculate the distance z by the relation:

( )

The resolution in distance is directly bound at the resolution in phase and in the

signal on noise ratio. When exceeds 2, there is an ambiguity on the measure of distance.

This limitation also exists in interferometry where a measure of distance comes down to a

measure of phase. To increase the extent of the measure without degrading the resolution,

it is frequent to use simultaneously or sequentially two frequencies of modulation. The

lowest frequency determines the reach of the rangefinder; the highest frequency

determines its resolution. For example, a rangefinder using two frequencies 5 and 50 MHz is

capable of making, if the signal on noise ratio is sufficient and when the phase is digitized on

8 bits, a non-ambiguous measure on 30 m with a 1 cm resolution. Popov and Yakovlev

realized a rangefinder working on natural target by using a diode laser InGaAs emitting at

0,85 µm a power of 10 mW, the reach of the system is about 30 m for a 1 mm resolution.

The current systems use several modulation frequencies and an algorithm of search, also, it

is necessary sometimes, to have more than one second to obtain a measure at the optimal

precision.

The problem of the electromagnetic coupling between the emission and the

reception and the problem of the multiple routes are the main limitations of these devices.

To limit the phenomena of crosstalk, diverse tricks were imagined. A first method consists in

feeding in a discontinuous way a diode laser and in realizing the measure of phase on diverse

harmonics of the photoelectric signal. An electro-optical device having a non-linear answer


30

Alexis Ratouis PAM8

compared with the signal of modulation was also used to realize the measure of phase on a

harmonic.

3.7.2. Telemetry modulation type “Chirp”

A modulation of the luminosity power of type "chirp" was recently used for diverse

applications of telemetry. The coding of the source consists in modulating linearly the

modulation frequency fm according to the figure 3-9.

The power emitted is:

( ) [ ( )]

With:

( )

for 0 < t < T

The mixture of a fraction of the wave emitted with the wave from the target supplies,

after an adequate filtering, a periodic signal of the type heterodyne, the frequency of which

is proportional at the distance. The mix of the signals can be made in an optical coupler or in

an electronic way. The advantage of this method results from the ease of implementation of

the optical part compared with the technique FMCW using a coherent detection. The main

limitation results from the complexity of the processing of the signal which has to extract

Reference Wave

Wave from the Target

Figure 3.9: Example of Scanning used in Telemetry Modulation type “Chirp”


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Alexis Ratouis PAM8

with a strong power of resolution in frequency the signal of beating which is generally

flooded in the background noise.

The results obtained with this method are very ill-assorted. The most convincing

measures concern the detection of natural targets by means of a system using a diode laser

GaAlAs emitting a power of the order of 100 mW at the wavelength of 817 nm, the reach is

of the order of 50 m and the resolution in distance is of the order of 25 cm. The time

necessary for processing of the signal limit the pace of the measures.

3.7.3. Time of Flight Telemetry

The impulsive telemetry with direct detection or time of flight telemetry consists in

emitting in the direction of the target an impulse of very short intense light, then in timing

the round way of this impulse. On the figure 3-10, ( ) represents the power emitted

towards the target and ( ) the power of the echo.

The time of flight measure is realized by a fast meter activated by the emission and

stopped at the reception of the impulse. The precision in distance depends on the duration

of the impulse and on the signal on noise ratio as it is indicated in the relation

and also of the resolution of the meter. We shall see later that the

height of the threshold of detection also plays a role in the calculation of the resolution.

Indeed, the determination of the moment of arrival of the impulse is realized by a

Threshold

Figure 3.10: Example of a Chronogram in Telemetry Time of Flight

Threshold


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Alexis Ratouis PAM8

comparator, the threshold of which is just situated over the noise (see paragraph 3.5). The

estimation of the moment of arrival thus depends on the level of the impulse of return. A

simple solution to solve this problem is to integrate several measures on the same point but

inevitably at the detriment of the pace of the measures.

In time of flight telemetry, the detection of the signal of return is realized in an

inconsistent way and the system of detection is based on the use of photodiodes with

avalanche effect. Yakovlev proposes a system of detection using a photodiode with

avalanche effect having a gain from 103 to 104 and conferring to the system a threshold of

sensibility of 1,7 109 W.Hz-1/2. The capacity of junction lower than 1,9 pF allows to obtain a

compatible bandwidth with the duration of the impulses of the order of 1 ns. The same

author presents a time of flight rangefinder which uses the photodiode with avalanche

described previously, and a circuit of interpolation which determines the fraction of unity of

counting between two knocks of the meter. He indicates that distances of 200 m are

measured with a precision from 5 to 10 mm according to the signal on noise ratio and this on

a diffusing target. It has been implemented a converter time - amplitude for the measure of

the time of flight. In taking the average value, they end up with a precision of the order of 1

mm for a range of measure from 0 to 2 m on non-cooperative target and of the order of 0,1

mm for a range of distance of 2,3 m in 4,4 m. Määttä et al show that time of flight

rangefinders remain successful in difficult conditions: they use a device with diode laser to

control profiles of high-temperature metallic surfaces (1400°C).

At the moment, advances regarding fast electronics and miniaturization of circuits

(ASIC), allow to develop time of flight rangefinders of low dimensions. Furthermore, since it

is possible for micro lasers to be activated passively and for diode laser to be low-cost, these

rangefinders are all the more compact and can aspire to processes of collective

manufacturing. The integration of the optical part and the electronics in the same box allows

to realize real microsystems, the utility of which is ceaselessly increasing in the consumer

domain. These micro rangefinders with eye safety work on every type of target, use a micro

laser Nd:YAG or Er:Glass and possess a reach about 100 m for a precision of the order of

about ten of cm.


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Alexis Ratouis PAM8

3.8. Triangulation

The telemetry laser with triangulation is not, a priori, a method of measure such as

we had defined it previously. Indeed, it does not use a parameter of modulation of the laser

source but geometrical information. However, numerous sensors using this method are in

the commerce, that is why we introduce it into this part.

The principle consists in transforming the information of longitudinal distance into a

transversal gap of the backscattered beam. The measure is then made by spotting this

position by means of a detector multipoint of type pin CCD, pin of photodiodes, or a

photodiode sensitive to the position.

Figure 3.11: Rangefinder using a pulse triggered micro laser passively

developed at Leti


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Alexis Ratouis PAM8

A laser source emits a beam collimated or focused at an intermediate distance in the

range of measure of the rangefinder. An optical system of reception re-focuses the

backscattered spotlight laser by the target on a pin CCD. The optical axis of the whole

reception is parallel to the axis of emission of the diode laser on the figure 3-12 by concern

of simplicity, but can be possibly inclined to optimize the formation of the image on the CCD.

Also, the pin CCD can be inclined by an angle ß compared with the optical axis to optimize

the depth of field of the optical system of reception. In this case, we show easily that:

(

)

The backscattered point laser by target and imaged on the CCD will be spotted in a position

δ dependent on the distance z of the target in the lens. We quickly find z:

(

)

The relation is not linear and the precision is not thus constant with the distance. In first

approximation, that is without taking into account the defocusing or the aberrations (coma

and distortion), it comes:

This type of sensor is thus more precise for the shortest distances. We find at the

moment pins CCD with 4096 pixels, and even 8192 pixels, which allows to obtain a good

resolution, that it also possible to improve by using an appropriate signal processing.

Target

Laser Beam

EMISSION BLOCK

RECEPTION BLOCK

Laser Source

CCD Detector

Figure 3.11: Principle of distance measurement by triangulation.


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Alexis Ratouis PAM8

Besides, these detectors can accumulate the signal on variable durations, what allows to

increase the signal on noise ratio and to detect very weak flows, thus to obtain interesting

reaches with weak luminosity sources. The main difficulty lies in the optics of reception

which must be generally opened enough to get back enough luminous flow while being

corrected by the aberrations on the axis and except axis on a vast domain of functioning.

This limits generally the range of distance of measure. Besides, these sensors are

cumbersome, the distance between the transmitter and the receiver that must be sufficient

to obtain an exploitable transversal gap.

The principle of detection is simple and especially adaptable to the range of distances

to be measured. We find in the literature and in the business of rangefinders with

triangulation working on a few centimeters with a precision which can come down till 10µm.

In conclusion, the triangulation is often applied to the industrial control of

dimensions or more generally in the precise measure of a distance around a given value,

where the depth of field is not a critical parameter.

3.9. Conclusion

This part allowed us to have a better comprehension of the techniques of laser

telemetry. Generally speaking, we noticed that the telemetry with coherent detection, that

is the telemetry which uses the principles derived from the interferometry, although having

a superior sensibility, has a conception much more complex than the telemetry with direct

detection. It is the simplicity of implementation and the reliability of the systems of direct

detection which allowed their marketing.


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Alexis Ratouis PAM8

Seeing the figure 3.12, it is clear that the system that we should use is of the

interferometry methods but because of the complex conception, it’s a method that we will

avoid. And our choice will be of a triangular system, which is also really precise and doesn’t

have the same problems as the FMCW.

So we will now try to find such a rangefinder in the commerce to see what can be

actually done with one of this sort and establish a list of characteristics of the product, which

will help us later to compare with other products using different systems, the ultrasonic and

infrared rangefinder.

4. Market of the Laser Rangefinder

We will now search among different enterprise the product, which will correspond to

our expectations.

4.1. Keyence Corporation

Keyence Corporation is a Japanese company which produces sensors, barcode

readers, vision systems, measuring equipment and digital microscopes.

Keyence is fabless (fabrication-less) - although it is a manufacturer; it specializes

solely in product planning and development and does not manufacture the final products.

Keyence products are manufactured at qualified contract manufacturing companies.

Time of Flight

Triangulation

Interferometry methods

FMCW

Rel

ativ

e E

rror

(%)

Figure 3.12: Range of distance and relative error of the main techniques of

Telemetry


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Alexis Ratouis PAM8

Of all the products that are offered, we will be interested by the LK-Series and LJ-

Series, these products are the rangefinder with triangulation system.

4.1.1. LK Series Laser Displacement Sensor

These rangefinders should be perfect for our need, they are using the triangulation

system and as we can see in the example of dimensions given by the figure 4.1, this

rangefinder is really small.

The LK CCD Laser Displacement Meter uses a triangulation measurement principle as

follows: A semiconductor laser beam is reflected off the target surface and passes through a

custom designed receiver lens system. The beam is focused on a CCD sensing array. The CCD

detects the peak value of the light quantity distribution of the beam spot. The CCD pixels

(individual CCD sensing elements) within the area of the beam spot are used to determine

the precise target position. As illustrated in the diagram above, as the target displacement

changes relative to the LK sensor head, the reflected beam position changes on the CCD

array. These positional changes are analyzed by the LK Controller which resolves height

changes as small as 10 microns.

Figure 4.1: LK-011 Sensor Head


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Alexis Ratouis PAM8

Figure 4.2: LK-2500 Series Long Range CCD Laser

Displacement Sensor Specification

1. Linearity was obtained using KEYENCE's standard target (Zirconia block gauge).

2. The LK-501 and LK-503 can both be used in High-precision mode or long-range

mode.


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Alexis Ratouis PAM8

Figure 4.3: LK Series High Accuracy CCD Laser

Displacemenr Sensor Specifications

1. Repeatability was obtained using KEYENCE's analog sensor controller (RD-50) with

the number of averaging measurements set to 64.Note: The ripple of the analog output

may be 1 mV or more due to common mode noise when observed with an oscilloscope

or a high-speed A/D conversion board.

2. Linearity was obtained using KEYENCE's standard target (Zirconia block gauge).


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Alexis Ratouis PAM8

4.1.2. LJ-Series: 2D Laser Displacement Sensor

This type of product could really be interesting because of the 2D measurement; it

could be a real gain of time. And level precision, there would be no better sensor.

Figure 4.4: LJ-G Series 2D Laser Displacement Sensor

Figure 4.5: LJ-G Series Sensor Head LJ-G030


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Alexis Ratouis PAM8

Figure 4.6: LJ-G 2D Laser Displacement Sensor,

Sensor Head Specifications

1. The value obtained after 64 times Averaging at the reference distance.

2. The target is KEYENCE standard object. (White diffusing material). The value is the average of the widths in

the Height mode.

3. The target is ø10 mm pin gauge. The value is the edge in the Position mode after 16 times of the Smoothing.

4. When the measuring range is the minimum in the initial setting.

5. The illumination on the receiver of the sensor head when targeting an illuminated white paper.


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Alexis Ratouis PAM8

4.2. Sensor Instruments GmbH

Sensor Instruments GmbH is a young company widening in the domain of the sensor.

As specialist for the specific detectors, Sensor Instruments GmbH has made a name for itself

at the national and international level.

The various technologies lasers (PSD, CCD), infrared, or white Leds, associated with

algorithms developed by theirs engineers lead in often unique and dedicated solutions.

The detection, the dimensional measure, the control of colors and aspects are the

domains in which Sensor Instruments will bring to the customer all its skills.

The laser rangefinder for a very precise measure of distance, working by triangulation

laser, proposes various distances and extents of measure. The CCD technology, associated

with the control of the methods of calculations of sub-pixels allows to obtain optimal

resolutions and quality of linearity without equal. A supplied software application, allows via

the serial port, to reach multiple parameters of regulations. By this way, available tools of

functioning allow to quantify the size of a part, its position, its movement … These sizes are

available in analog values 4 / 20mA, 0 / 10V or digital.

So we will look at a certain category of products: The L-LAS—LT. High-resolution

laser of 4096 points proposed in range of measure from 4mm (1µm) to 700mm (200µm). All

the features are available to be able to aspire to the biggest performance.


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Alexis Ratouis PAM8

Of these two enterprises, the one to stand really out are the product of the Keyence

Corporation. They are way more precise and the second one, the product of the LJ-Series

with the 2D Laser Displacement Sensor, could be really better for almost any use that we will

make of them. But we can assume that they will be more costly. (The catalogue of the

company is available online at the internet link of the Keyence Corporation:

http://www.keyence.de/)

We will now study the market of the ultrasonic and infrared sensor.

5. Market of the Ultrasonic and Infrared Sensor

The first thing that we observed was that the market of the ultrasonic and infrared

sensor were not as provided as the market of the laser sensor and that the quality

(precision) of the ultrasonic sensor are generally way smaller than the laser sensor. They are

more made with the purpose to detect an object but not really to measure it.

But we will nevertheless present some of these sensors.

5.1. Ultrasonic Sensor

Like previously explain, the ultrasonic sensor is not one of the most precise sensor

that we can find. In the figure 5.1, we can see the functioning of one of these sensors.

Reference Measuring Range Resolution

L-LAS-LT-37 35…39mm 1µm



L-LAS-LT-110 90…130m 12µm

L-LAS-LT-135 110…174mm 16µm

L-LAS-LT-160 125…195mm 20µm

L-LAS-LT-200 162…258mm 25µm

L-LAS-LT-275 200…415mm 55µm

L-LAS-LT-450 285…950mm 200µm

Figure 4.7: L-LAS-LT

http://www.keyence.de/


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Alexis Ratouis PAM8

Sensor

Modul

Alimentation

Analogic

Input

4 Switches

Potentiometer 8 Switches

Figure 5.1: Synchronizable Ultrasonic Sensor


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Alexis Ratouis PAM8

Scale drawing Detection zone

1 x pnp + 1 x analogue 4-20 mA / 0-10 V

350 mm

Operating range Design Operating mode Particularities

30 - 250 mm Cylindrical M30 Proximity switch/reflective mode Reflective barrier Window mode Analogue distance measurement Display

Ultrasonic -specific

Means of measurement Transducer frequency Blind zone Operating range Maximum range Angle of beam spread Resolution/sampling rate Reproducibility Accuracy

Echo propagation time measurement 320 kHz 30 mm 250 mm 350 mm Please see graphics detection zone 0.025 mm to 0.10 mm, depending on the analogue window ± 0.15 % ± 1 % (temperature drift internally compensated)

Electrical data

Operating voltage UB Voltage ripple No-load current consumption Type of connection

9 - 30 V d.c., reverse polarity protection ± 10 % ≤ 80 mA 5-pin M12 initiator plug

mic+25/DIU/TC


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Alexis Ratouis PAM8

Outputs

Output 1 Output 2 Switching hysteresis Switching frequency Response time Delay prior to availability

Analogue output Current: 4-20 mA / voltage: 0-10 V (at UB ≥ 15 V), short-circuit-proof Switchable rising/falling Switching output pnp: Imax = 200 mA (UB-2V) NOC/NCC adjustable, short-circuit-proof 3 mm 25 Hz 32 ms < 300 ms

Inputs

Input 1

com input Synchronisation input

Housing

Material Ultrasonic transducer Class of protection to EN 60529 Operating temperature Storage temperature Weight Further versions Further versions

Brass sleeve, nickel-plated, plastic parts, PBT, TPU Polyurethane foam, epoxy resin with glass contents IP 67 -25°C to +70°C -40°C to +85°C 110 g Stainless steel Cable connection (on request) mic+25/DIU/TC/E

Technical features/Characteristics

Temperature compensation Controls Scope for settings Synchronization Multiplex Indicators Particularities

Yes 2 push-buttons + LED display (TouchControl) Teach-in and numeric configuration via TouchControl LCA-2 with LinkControl Yes Yes 3-digit LED display, 2 x three-colour LED Display

Documentation (download)

Pin assignment

Figure 5.2: Properties of an Ultrasonic Sensor of the Microsonic Company: mic+25/DIU/TC


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Alexis Ratouis PAM8

The figure 5.2 presents an ultrasonic sensor of the Microsonic Company. It was the

best one in the market of the ultrasonic rangefinder.

We will now study the market of the infrared sensor.

5.2. Infrared Sensor

First of all, we will see in the next figure (5.3) a comparison between infrared and

ultrasonic sensor.


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The Principle

Rangefinders with ultrasounds work by measuring the time of return of an inaudible sound wave emitted by the sensor. The speed of sound in the air being about stable, we deduct the distance from the obstacle.

The sensor SHARP works by measuring the angle of reflection of a emission of modulated IR, thanks to receiver's row.

The Reach

Generally some meters for the systems ultrasounds, even if in theory there is no limit. There is also a minimal distance.

The reach is between 5 to 80 cm.

The Directivity

The ultrasounds are very evasive. What can be a big advantage (detection of obstacle moved closer on a wide crown) or a big inconvenience (detection of the walls of a corridor and not the end of the corridor).

The directivity is much better (cone of 5 °). To have better, it is then necessary to take rangefinders laser which are much more expensive!

The Precision

The precision of the ultrasounds depends on the precise measure of the time of route of the sound wave. The latter can also vary according to the conditions of temperature, pressure...

The precision of the sensor depends on the distance. Excellent at 10 cm, it declines more and more up to the 80cm.

The Size

Transducers ultrasounds can be rather small. But cards realizing the telemetry as take up some room.

The size is very small. Nothing else is necessary.

The Consummation

100 mA in sleep mode and up to several Amperes in emission.

Only 25 mA

The Price

Several tens of euro. (It is necessary to have the module of command and a transducer)

From approximately 15 €

Soundwaves


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The connection with a micro-controller

There is in fact 2 different version: The sensor has an analog exit. The sensor has a kind of serial connection, very easy to code on a microcontroller.

Frequency and speed of acquisition

The sensor in analog version send a measure all 40ms.

Sensibility to interferences and to other sensors

We saw it previously, the sensors ultrasounds are sensitive to the temperature and to the pressure. But there is more serious: they are also sensitive to the other devices using the same frequencies, or simply the other robots!

This sensor IR has a modulation which frees them normally from the ambient lighting.

Who uses them?

“Professional” robots use the sensors with ultrasounds a lot. But it is always very complicated to model totally an environment according to their return, in particular because of the too important cones of emission.

Toys manufacturers Pob Technology

Conclusion

Obviously, both systems have their advantages and their inconveniences, and if the distance is an information which interests us we will need to choose between both. Having said that, we would distinguish 4 cases:

- The IR sensor are what is simpler there! - If we need to measure a distant distance, and only the ultrasounds will allow it. But

Attention on the wide cone of emission! - We really want to be sure that nothing approaches near our robot, and in this case

multiple ultrasounds sensors will cover better that the IR. - We have a small robot, with little room, not a lot of autonomy. Here obviously, the

IR will suit better.

Figure 5.3: Board of Comparison between the Ultrasound and Infrared Sensors


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And here is an example offered by the Go Tronic Company:

Now that we have a better idea of what kind of sensors we can find, we can make a

choice on which type of sensor we want to use.

Infrared sensor with double element

possessing a big sensibility of

detection.

Applications: detector of presence,

alarm, home automation, infrared

switch, etc.

Temperature of service(department): 40 °C in 80 °C Alimentation: 2.2 Vcc to 15 Vcc Consumption: 15 µA Field of detection: 52 ° x 52 ° Case: TO5

Figure 5.4: Infrared Sensor: IRAE700


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6. Conclusion

We will begin the conclusion with a little summary of the differences between the

three sorts of sensors (see figure 6.1).

Seeing this board we conclude that the Laser Rangefinder is really the best choice

that we could make and we should use a sensor of the LJ-Series (2D laser displacement

sensor) of the Keyence Company. Its system would be a real help to identify the object in our

close room.

With this sensor, we will have many advantages, it is already built, there is a program

given with it to process the informations given by the sensor, the technology 2D will allow a

major gain of time,… The only inconvenient will be the price, but we think that it is worth it.

Ultrasonic Infrared Laser

Reach From 1 to 250 cm From 5 to 80 cm Several meters to several tens of meters according to the models.

Directivity Cone about 30 ° Cone about 5 ° The most directive (of the order of the degree, even of the half-degree)

Precision Relatively precise but the precision decreases with the distance, the angle of measure and the conditions of temperature and pressure.

Relatively precise but the precision decreases with the distance.

Are precise with a noise of some centimeters on measures of several meters.

Cost Cheap Cheap Relatively expensive Sensibility to Interferences

Sensitive to the temperature and to the pressure. Also sensitive to the other robots using the same frequency which can lead to some problems in a competition.

Are sensitive to the strong light sources which contain a strong infrared radiation. Are also sensitive to the color and to the nature of the obstacles.

Cannot detect objects reflecting the light (windows, chrome-plated objects)

Figure 6.1: Board of Comparison between the Ultrasound, Infrared and Laser Sensors


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7. Sources

Generality:

www.univ-rouen.fr/psi/heutte/rdf/Introduction.pdf

http://www.immersion.fr

http://www.ino.ca/fr-ca/expertise/capteurs-3D.html

http://www.lapresse.ca/sports/200809/08/01-664024-lavantage-des-telemetres.php

http://www.generationrobots.com/fr/content/65-les-capteurs-a-ultrasons-pour-les-robots

http://www.robotshop.com/comparatif-capteurs-distance-infrarouges-ultrasonique.html

http://www.acgrenoble.fr/college/henri.corbet/file/Technologie/4ieme/Confort_Domotique

/CI_6/webprof/res/Comparatif_Capteurs_ultrason_IR.pdf

Laser Sensor :

Wikipédia :

Télémètre laser

Laser rangefinder

Abstandsmessung (optisch)

http://www.forum-outillage.com/bricoler-outillage-maison-plateau-ponceuse-excentrique-

black-decker.htm

http://www.nextag.fr/laser-mesure-distance/recherche-html

http://www.pce-instruments.com/french/instruments-de-mesure/mesureurs/t-l-m-tres-

laser-kat_132053_1.htm

http://www.bosch.fr/presse/communique.asp?id=317

http://technoptronique.free.fr/assets/files/analyse_technique/telemetre_laser/telemetre_la

ser.pdf

https://artemis.oca.eu/spip.php?article303

http://www.femto-st.fr/~jdudley/opto/so_oe10telemetlaser.htm

http://augereau.robot.free.fr/fichiers/not_used/theorie_telemetrie/soutenance.pdf

http://www.univ-rouen.fr/psi/heutte/rdf/Introduction.pdf

http://www.immersion.fr/

http://www.ino.ca/fr-ca/expertise/capteurs-3D.html

http://www.lapresse.ca/sports/200809/08/01-664024-lavantage-des-telemetres.php

http://www.generationrobots.com/fr/content/65-les-capteurs-a-ultrasons-pour-les-robots

http://www.robotshop.com/comparatif-capteurs-distance-infrarouges-ultrasonique.html

http://www.acgrenoble.fr/college/henri.corbet/file/Technologie/4ieme/Confort_Domotique/CI_6/webprof/res/Comparatif_Capteurs_ultrason_IR.pdf

http://www.acgrenoble.fr/college/henri.corbet/file/Technologie/4ieme/Confort_Domotique/CI_6/webprof/res/Comparatif_Capteurs_ultrason_IR.pdf

http://www.forum-outillage.com/bricoler-outillage-maison-plateau-ponceuse-excentrique-black-decker.htm

http://www.forum-outillage.com/bricoler-outillage-maison-plateau-ponceuse-excentrique-black-decker.htm

http://www.nextag.fr/laser-mesure-distance/recherche-html

http://www.pce-instruments.com/french/instruments-de-mesure/mesureurs/t-l-m-tres-laser-kat_132053_1.htm

http://www.pce-instruments.com/french/instruments-de-mesure/mesureurs/t-l-m-tres-laser-kat_132053_1.htm

http://www.bosch.fr/presse/communique.asp?id=317

http://technoptronique.free.fr/assets/files/analyse_technique/telemetre_laser/telemetre_laser.pdf

http://technoptronique.free.fr/assets/files/analyse_technique/telemetre_laser/telemetre_laser.pdf

https://artemis.oca.eu/spip.php?article303

http://www.femto-st.fr/~jdudley/opto/so_oe10telemetlaser.htm

http://augereau.robot.free.fr/fichiers/not_used/theorie_telemetrie/soutenance.pdf


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Alexis Ratouis PAM8

http://www.sgc.ethz.ch/sgc-volumes/sgk-79.pdf

http://www.sensorinstruments.fr/produits/telemetres-lasers.html

http://www.keyence.de/products/measure/laser/laser.php

http://champs.cecs.ucf.edu/Library/Journal_Articles/pdfs/Axelsson_Processing_of_Laser_Sca

nner_Data.pdf

Ultrasonic Sensor :

http://l.lefebvre.free.fr/tele/tele_01.html

http://perso.crans.org/pierre/documents/Telemetre_a%A0_ultrasons.pdf

http://public.iutenligne.net/etudes_realisations/Montagny/telemetre/index.html

http://vigienature.mnhn.fr/sites/vigienature.mnhn.fr/files/uploads/PaulineVANLAERE_dossie

r.pdf

http://shopping.cherchons.com/dossier/telemetre-a-ultrasons.html

http://www.interface-z.com/pronfiture/telemetres-ultrason/83-telemetre-ultrason-sp.html

http://www.interface-z.com/produits/cap05_ultrason.htm

http://jrzp.files.wordpress.com/2011/04/renesas_app_note_ultrasonic_range_finder.pdf

https://www.sparkfun.com/products/639

http://www.extech.com/instruments/resources/manuals/DT100_UMfr.pdf

http://www.microsonic.de/

http://www.microsonic.de/DWD/_111327/pdf/1033/microsonic.pdf

http://www.parallax.com/

http://www.interface-z.com/pronfiture/telemetres-ultrason/84-telemetre-ultrason-

synchronisable-3-ana.html

http://www.microsonic.de/en/Products.htm

http://www.bannerengineering.com/en-US/products/8/Sensors/30/Ultrasonic-

Sensors/101/U-GAGE-QT50U-Ultrasonic-Sensors/

http://www2.aclyon.fr/etab/lycees/lyc69/descartes/IMG/pdf/Capteur_ultrasonique_Li2oc.p

df

http://www.sgc.ethz.ch/sgc-volumes/sgk-79.pdf

http://www.sensorinstruments.fr/produits/telemetres-lasers.html

http://www.keyence.de/products/measure/laser/laser.php

http://champs.cecs.ucf.edu/Library/Journal_Articles/pdfs/Axelsson_Processing_of_Laser_Scanner_Data.pdf

http://champs.cecs.ucf.edu/Library/Journal_Articles/pdfs/Axelsson_Processing_of_Laser_Scanner_Data.pdf

http://l.lefebvre.free.fr/tele/tele_01.html

http://perso.crans.org/pierre/documents/Telemetre_a%A0_ultrasons.pdf

http://public.iutenligne.net/etudes_realisations/Montagny/telemetre/index.html

http://vigienature.mnhn.fr/sites/vigienature.mnhn.fr/files/uploads/PaulineVANLAERE_dossier.pdf

http://vigienature.mnhn.fr/sites/vigienature.mnhn.fr/files/uploads/PaulineVANLAERE_dossier.pdf

http://shopping.cherchons.com/dossier/telemetre-a-ultrasons.html

http://www.interface-z.com/pronfiture/telemetres-ultrason/83-telemetre-ultrason-sp.html

http://www.interface-z.com/produits/cap05_ultrason.htm

http://jrzp.files.wordpress.com/2011/04/renesas_app_note_ultrasonic_range_finder.pdf


http://www.extech.com/instruments/resources/manuals/DT100_UMfr.pdf

http://www.microsonic.de/

http://www.microsonic.de/DWD/_111327/pdf/1033/microsonic.pdf

http://www.parallax.com/

http://www.interface-z.com/pronfiture/telemetres-ultrason/84-telemetre-ultrason-synchronisable-3-ana.html

http://www.interface-z.com/pronfiture/telemetres-ultrason/84-telemetre-ultrason-synchronisable-3-ana.html

http://www.microsonic.de/en/Products.htm

http://www.bannerengineering.com/en-US/products/8/Sensors/30/Ultrasonic-Sensors/101/U-GAGE-QT50U-Ultrasonic-Sensors/

http://www.bannerengineering.com/en-US/products/8/Sensors/30/Ultrasonic-Sensors/101/U-GAGE-QT50U-Ultrasonic-Sensors/

http://www2.aclyon.fr/etab/lycees/lyc69/descartes/IMG/pdf/Capteur_ultrasonique_Li2oc.pdf

http://www2.aclyon.fr/etab/lycees/lyc69/descartes/IMG/pdf/Capteur_ultrasonique_Li2oc.pdf


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Infrared Sensor :

http://robot.campus.ec-nantes.fr/wordpress/wp-content/uploads/2009/01/sharp.pdf

http://www.smartec.nl/infrared_sensor.htm


http://www.gotronic.fr/art-capteur-infrarouge-irae700-2540.htm

https://robot.campus.ec-nantes.fr/wordpress/wp-content/uploads/2009/01/sharp.pdf

http://en.wikipedia.org/wiki/Infrared_detector

http://fr.wikipedia.org/wiki/D%C3%A9tecteur_infrarouge

http://robot.campus.ec-nantes.fr/wordpress/wp-content/uploads/2009/01/sharp.pdf

http://www.smartec.nl/infrared_sensor.htm


http://www.gotronic.fr/art-capteur-infrarouge-irae700-2540.htm

https://robot.campus.ec-nantes.fr/wordpress/wp-content/uploads/2009/01/sharp.pdf

http://en.wikipedia.org/wiki/Infrared_detector

http://fr.wikipedia.org/wiki/D%C3%A9tecteur_infrarouge

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