EP3458875A1

EP3458875A1 - Optical telemetry system

Info

Publication number: EP3458875A1
Application number: EP17727643.3A
Authority: EP
Inventors: Bastien BECHADERGUE; Luc Chassagne; Hongyu GUAN
Original assignee: Universite de Versailles Saint Quentin en Yvelines; Institut Vedecom
Current assignee: Universite de Versailles Saint Quentin en Yvelines; Institut Vedecom
Priority date: 2016-05-19
Filing date: 2017-05-10
Publication date: 2019-03-27
Also published as: FR3051560A1; US20190204444A1; CN109844565B; FR3051560B1; US11255971B2; CN109844565A; WO2017198927A1

Abstract

The present invention relates to an optical telemetry system for measuring the distance between two vehicles comprising a first optoelectronic assembly formed by at least one light source SL_s and at least one photosensitive sensor CP+ which source and sensor are oriented towards in front of the vehicle, and a second optoelectronic assembly formed by at least one light source SL_c (6) and at least one photosensitive sensor CP_c (5) that is oriented towards behind the vehicle, characterized in that said light sources SL_s and SL_c are conventional light sources, the light source SL_s being modulated by a signal of frequency F_s, said light source SL_c (6) of the target (4) being modulated by a clock of frequency controlled by a phase-locked loop driven by the electrical signal delivered by said photosensitive sensor CP_c, said first optoelectronic assembly furthermore comprising a circuit for measuring the phase shift between the electrical signal delivered by said photosensitive sensor CPS (5) and the signal modulating the paired light source SL_s (6), said system furthermore comprising a computer for determining the distance depending on the frequency F_s and the measured phase shift. The invention also relates to an optoelectronic assembly for an optical telemetry system, to a vehicle equipped with such a system and to a telemetry method.

Description

OPTICAL TELEMETRY SYSTEM

The present invention claims the priority of the French application 1654486 filed May 19, 2016 whose content (text, drawings and claims) is hereby incorporated by reference.

Field of the invention

The present invention relates to the field of optical telemetry, for the evaluation of distance between a few tens of centimeters and a few tens of meters, and more particularly a distance measuring system between two moving objects such as robots or motor vehicles. which follow each other.

This system can complement the FMCW radar technologies already deployed (but sensitive to interference) or LIDAR (still little deployed because relatively expensive) for short distance applications and dense traffic as the grouping of vehicles by platoon convoys road (in English platooning ).

However, the principle can be extended to fields of application other than the automobile, for example for displacement trolleys used in a factory or industrial robots.

State of the art It is known in the state of the art to

numerous telemetry solutions, based on the use of sound or ultrasound waves, radio-electric or light electromagnetic waves.

In the latter category, there are known rangefinders using a laser source.

Two distance measurement techniques are

Generally used in the automobile:

The coherent detection.

Direct detection by measurement of flight time. The coherent detection method is used in FMCW (Frequency Modulation) type radar systems

Continuous-Wave) whose principle is as follows: a signal whose frequency is modulated in sawtooth is emitted by the system. This signal is then reflected by the target whose distance to the system is to be measured. The echo received by the system has a frequency offset proportional to the system / target distance. This type of radar uses coherent radio waves.

Direct detection by time of flight measurement is used in Ultra-Wide Band Radar systems

(UWB), where the carrier wave is a radio wave, and LIDAR, where the carrier wave is a light wave, usually

monochromatic, infrared and coherent. It can also be used with (ultra) sound waves (for reversing sensors for example). Two methods are used for the measurement of flight time:

The direct measurement of flight time, the principle of which is simple: when the wave is emitted by the system, a counter is triggered. When echo reflected by the target is received, this counter is stopped. The time thus measured corresponds to the round trip time of the transmitted wave and is therefore proportional to the system / target distance. The indirect measurement by phase shift measurement, whose principle is similar: a periodic signal is emitted at a fixed frequency. The echo reflected by the target is received by the system with a phase shift directly

proportional to the system / target distance. When the carrier wave is an optical wave, European patent application EP2962127 is known in particular concerning a method for determining a distance of an object with respect to a motor vehicle by using a PMD sensor, comprising the following steps : - in a measurement cycle, measurement of a phase shift of a measurement signal

reflected by the object for at least one frequency of

modulation,

said modulation frequency being chosen so as to make it possible from this phase shift to determine unequivocal distance within a range of range starting at the level of the motor vehicle, and measuring the propagation time of an individual signal reflected by the object during a

time interval that starts with the individual signal and ends at a point of time corresponding to twice the range range

if an individual reflected signal has been measured during the time interval, determining a distance from the phase shift;

- if no individual reflected signal has been measured during the time interval, rejection of the phase shift without distance determination.

European Patent EP0300663 describes another example of an optical telemeter using a light source modulated by continuous amplitude modulation, a sensor for collecting a portion of the optical energy returned by an object, and means for measuring the distance to the light. object by detecting the phase difference between the

modulating the radiated optical energy and modulating the returned optical energy, including means for compensating for changes in the level of the returned optical energy.

It is also known, in a context which does not concern the measurement of the distance between two mobile vehicles but the measurement of the determination with a high accuracy of the position of a moving object with respect to a fixed terminal, a method described in the European Patent Application EP0961134.

This document describes a roadway system

automated system comprising transponders or data stations spaced at known positions along the

floor. This pavement system allows a vehicle to determine its position as it moves along the roadway. Each vehicle is equipped with a transmitter

transmitting a spread spectrum transmission signal which is pseudo (PN) coded. The transmitted signal is received by the transponder from a terminal disposed along the roadway. This transponder transmits a response signal to a receiver carried by a vehicle. The receiver also receives a second signal which may be a response signal from the same transponder or a response signal from an adjacent transponder. The system then measures a difference in time between the transmission of the interrogation signal originating from the vehicle and the reception of its corresponding response signal to determine the distance between the vehicle and the transponder or the reflector. Based on the determined distances, positions of the transponders and the distance traveled by the vehicle during its communications, the position of a vehicle is determined using

triangulation.

Also known are UCHIDA publications and "A vehicle to vehicle communication and ranging system-based spread spectrum technical-SS radar communication" published in "Vehicle Navigation and Information Systems Conference 1994, Proceeding Yokohama Jeapn August 31, 1994 ISBN 978-7803 -2105- 2 "or MIZUI et al" ISSN 8756-6621 or SUZUKI et al. "IEEE ICVES XP032866885 V2V communication and ranging system." These articles propose solutions based on laser beams emitting a monochromatic and coherent light to measure the distance between two vehicles.

Disadvantages of the Prior Art The solutions of the prior art provide

It is imperative to use coherent and directional light sources to avoid external disturbances. The reflected signal is, with such sources, certainly noisy but sufficiently powerful and "clean" to ensure the distance measurement over several tens of meters.

However, these sources are expensive and require the addition of an additional optical component with respect to

the usual equipment of a car, for example an additional laser source or LED integrated on the vehicle.

The solutions of the prior art do not make it possible to use sources that are already integrated into a

vehicle for other functions, such as front and rear lights. Indeed, these sources are polychromatic, not coherent and dispersive, and induce a problem of attenuation of the signal after reflection.

Another disadvantage of the prior art solutions is that they are susceptible to interference generated by similar adjacent systems. If the system X sends a signal and receives that of the system Y and not the desired echo, the measurement will be distorted. This is why PN codes are used. This solution certainly avoids collisions between the signals emitted by two vehicles in the same detection zone of a terminal, but requires the individualization of the code equipping each

vehicle. For a frame length of given PN signals, the number of available codes is limited, and therefore allows to equip a limited number of vehicles with a unique code. The increase in the length of the frame certainly makes it possible to increase the number of vehicles that can be

equipped, but then involves computer processing for the calculation of heavy and slow autocorrelation.

Moreover, such a solution requires a coherent and monochromatic light signal to avoid interference by the stray light and is not suitable for sending signals in white or non-colored light.

consistent.

Solution provided by the invention

In order to remedy these drawbacks, the invention relates in its most general sense to an optical telemetry system according to claim 1 and to the dependent claims.

For the purposes of this patent, the term "conventional light source" means a source of electrical light that is not a laser beam. The conventional light sources implemented by the invention are not at the same time

monochrome, directive and consistent. Will be a

"Conventional light source" within the meaning of this patent, in particular a white or colored light-emitting diode, a matrix or a set of LEDs, or an electric incandescent lamp, or a vehicle headlight or a traffic light.

The invention also relates to a telemetry method according to the claims.

Detailed description of a non-limiting example of

The present invention will be better understood on reading the detailed description of a nonlimiting example of the invention which follows, with reference to the accompanying drawings, in which: FIG. 1 represents a schematic view of a system according to FIG. invention

FIG. 2 represents the schematic diagram of the

optoelectronic assemblies

Figures 3 and 4 show the signals measured at different points of the system. General principle of the invention

Figure 1 shows a schematic view of a system according to the invention. The follower vehicle (1) is equipped with a light-emitting diode headlamp (2) emitting a beam (3) towards a tracked vehicle (4).

This vehicle is equipped with a sensor (5) and a light emitting light source (6) emitting a beam (7) in the direction of the follower vehicle (1), equipped with a sensor (8).

In the first example described, the first optoelectronic assembly is formed by a single light source SL _s and a single photosensitive sensor CP _s both oriented towards the front of the vehicle. The second optoelectronic assembly formed by a single light source SL _o (6) and a single photosensitive sensor CP _o (5) facing the rear of the vehicle.

The term "a single conventional source" may designate an LED for example, or a matrix of LEDs forming a lighthouse or a traffic light. Schematic diagram of optoelectronic assemblies

The follower vehicle (1) is equipped with an optoelectronic assembly comprising an LED light source (2) powered by a power supply circuit - driver in English -

(10). This supply circuit (10) is controlled by a square wave generator (11) delivering a modulation signal at a frequency of 1 MHz, in the example described. This modulation frequency is preferably between 0.5 and 10 MHz.

The transmitted light signal is, when received by the sensor (5) of the vehicle followed or target (4), attenuated and tainted noise.

The sensor (5) of the tracking or target vehicle (4) delivers a noisy electrical signal to a processing circuit (12) comprising an amplification stage and a filtering stage of the received signal and then a comparison stage for reconstructing the square signal. issued. This square signal is transmitted to a phase lock loop (Phase Lock Loop) to enslave an oscillator (13) whose phase is identical to that of the reconstructed signal. The frequency of this oscillator (13) is identical to that of the oscillator

(11), or a multiple or sub-multiple of this frequency.

This treatment makes it possible to restore a signal having a form factor close to that of the signal emitted by the light source (2) of the follower vehicle, and to eliminate the noise induced by the parasitic lighting coming from the road lights, the ambient light or various reflections that can illuminate the sensor of the vehicle followed.

The re-transmitted signal (14, 6) is received by the sensor (8) of the follower vehicle (1) and then processed by a circuit (15) to be reconstructed as a square signal. This reconstructed signal is then transposed to a lower intermediate frequency by a heterodyne mixer circuit (16).

The output of the circuit (16) is used as input of a microcomputer (17) controlled by a phase shift measurement algorithm. The signal transmitted in the first place is also transposed to the intermediate frequency to be compared, during the phase shift measurement, with the signal received by the follower and heterodyned vehicle.

Unlike FMCW radars or LIDAR / ultrasonic sensors, the system according to the example of the invention described in a non-limiting manner is based on the use of white light produced by vehicle LED headlights, or of color for light. produced by other traffic lights.

This light is polychromatic and non-coherent.

Consequently, the wave reflected by the target will be much more attenuated than in the case of a coherent wave so that it is impossible for the system to work directly with the reflected wave.

Its principle, summarized in Figure 3, is as follows: here we have two sensors A and B. The sensor A emits a sinusoidal signal at the frequency f ₁ . This signal is received by the sensor B with a delay t _AB . B then locks in frequency and in phase on the signal, and generates, thanks to a PLL, a signal of the same phase shift but of frequency f ₂ proportional to f ₁ then emits it. This signal may possibly have a delay due to the processing electronics. This new signal is received by A with a delay t _AB which is added to the phase shift already present. A locks then in frequency and in phase and can compare the phase of the signal that it emitted with that of the one on which it is locked: the phase shift and thus the distance are thus recovered. Once the phase shift is recovered, it must be measured to go back to the distance data. The method used to measure the phase difference is given for information only.

The method described is based on a clock pulse counter. The principle of this method is shown in Figure 4. The signal from the system is in this figure denoted E 'f _m and the reflected signal received by the system is noted E'if _r . Note that these two signals are out of phase and that the corresponding phase shift signal is noted E _d . A frequency clock _fcp much greater than the frequency of the transmitted signal is then used in an AND logic gate with the signal E ^ _d to obtain the signal presented on the last line. By counting the number of rising edges of this signal, it is thus possible to measure the width of each high state of the signal E ^ _d and thus to measure the value of the phase shift. This approach, however, introduces a compromise: the higher the frequency of the transmitted signal, the better the theoretical resolution of the distance measurement. However, for a fixed _fcp frequency, the higher the frequency of the transmitted signal, the lower the resolution of the phase shift measurement by clock counter. To overcome this problem, a conventional technique consists in transmitting the signal at a high frequency and then transposing the echo received at a lower frequency before processing it, according to the heterodyne processing principle based on the multiplication of several frequencies combined by a mixer.

Taking into account the calculation time

The treatment carried out to calculate the distance may take into account, to improve the relevance of the

calculation, the delay introduced by the processing circuit (12) ensuring the denoising of the signal received by the sensor of the

vehicle followed, to control the signal emitted by the vehicle followed.

This delay can be taken into account in the form of a fixed parameter taken into account for the calculation of the distance. This fixed parameter is determined experimentally or by modeling as a function of the nominal processing time of the processing circuit (12).

It can also be constituted by a variable parameter which can be updated periodically, for example in the case of change of technologies of treatments on vehicles.

It can also be updated by learning according to other telemetry data of the distance between the follower vehicle and the tracking vehicle available on the follower vehicle, for example geolocation data of the two vehicles received by the follower vehicle, or data from other telemetry equipment, for example systems using a laser or sound source.

Variants for signal coding

The signal controlling the light source of one and / or the other vehicle may further be coded to transmit information such as the speed of the vehicle, or a braking identity or information, or possibly the date and time, or a

distance information, by comparison

of clocks.

This coding may be a Manchester type encoding, also called two-phase coding or PE (for Phase Encode), introducing a transition in the middle of each interval. It consists in making an exclusive OR (XOR) between the signal and the clock signal, which results in a rising edge when the bit is at zero, a falling edge in the opposite case.

It may also be a coding of the type "coding of pairs of four-bit values in pairs of six-bit symbols" as described for example in the European patent EP0629067.

Such a type of coding is basically

different from a pseudo-random coding described in patent EP0961134.

The coded information may for example include information on the actuation of braking or

acceleration by a vehicle, during a convoy journey, for propagation of this information to the follower vehicles. Variants for measuring the lateral distance

The described implementation example makes it possible to provide the distance along the longitudinal direction, on the right between the optoelectronic assembly equipping the follower vehicle and the optoelectronic assembly equipping the vehicle being tracked.

It is possible to provide information

additional information concerning the lateral shift of the two

vehicles, for example to provide information on the preparation of an overtaking or flipping in another lane.

According to this variant, different combinations can be envisaged:

a) The follower vehicle may comprise an optoelectronic assembly formed by a light source SL _s and two photosensitive sensors CP _s , for example disposed on either side of the front of the vehicle, while the vehicle followed, constituting the target, comprises an optoelectronic assembly formed by at least one light source SL _o and a photosensitive sensor CP _o discarded

b) The follower vehicle may comprise an optoelectronic assembly formed by two light sources SL _s

staggered, for example on both sides of the front of the

vehicle, and two photosensitive sensors CP _s , while the vehicle followed comprises an optoelectronic assembly formed by two light sources SL _o and two photosensitive sensors CP _o spaced, for example arranged on either side of the rear of the vehicle.

In this case, each of the light sources SL of the follower vehicle and the source located on the same side on the tracked vehicle is modulated with a specific frequency F.

Claims

claims

1 - Optical telemetry system for measuring the distance between two vehicles comprising:

• a first optoelectronic assembly formed by at least one light source SL _s and at least one photosensitive sensor CP _s oriented in a first direction of the vehicle, and

A second optoelectronic assembly formed by at least one light source SL _o (6) and at least one sensor

photosensitive CP _o (5) oriented in the opposite direction of the vehicle,

characterized in that

• said light sources SL and SL are conventional light sources, the light source SL _s being modulated by a signal of frequency F _s,

Said light source SL _o (6) of the target (4) being

modulated by a frequency clock controlled by a phase-locked loop driven by the electrical signal delivered by said photosensitive sensor CP _o

Said first optoelectronic assembly comprising in

in addition to a circuit for measuring the phase difference between the electrical signal delivered by said photosensitive sensor CP _S (5) and the modulation signal of the light source SL _s (6) coupled,

Said system further comprising a calculator for

determine the distance as a function of the frequency F _s and the measured phase shift. 2 - Optical telemetry system according to

claim 1 characterized in that said light source SL _s of the first optoelectronic assembly is directed towards the front of the vehicle and is constituted by the LED headlights of a vehicle emitting a white light.

3 - Optical telemetry system according to

Claim 1 characterized in that said light source SL _o of the second optoelectronic assembly is directed towards the rear of the vehicle and is constituted by a traffic light of a vehicle emitting a colored light.

4 - optical telemetry system according to claim 1 characterized in that the modulation signal is a rectangular signal.

5 - optical telemetry system according to claim 1 characterized in that the modulation signal is a sinusoidal signal.

6 - optical telemetry system according to claim 1 characterized in that at least one of the optoelectronic assemblies comprises a signal processing circuit for reconstructing a signal corresponding to the nominal form from the light signal received by the sensor photosensitive.

7 - optical telemetry system according to claim 1 characterized in that the measurement of the phase shift is performed by a heterodyne circuit.

8 - optical telemetry system according to claim 1 characterized in that the sets

optoelectronic devices include an opaque cover preventing direct transmission between the light source and the photosensitive sensor.

9 - optical telemetry system according to claim 1 characterized in that said light source SL _o of the target is modulated by a frequency clock F _o , one of the frequencies F _s , F _o being multiple of the other, the first optoelectronic assembly comprising a circuit for filtering the signal delivered by the photosensitive sensor CP _s by a filter reducing the amplitude of the frequency signals F _s .

10 - optical telemetry system according to claim 1 characterized in that at least one of said Optoelectronic assemblies comprises a modulated signal coding circuit.

11 - optical telemetry system according to claim 1 characterized in that the first optoelectronic assembly directed towards the front of the vehicle is formed by a light source SL _s and two photosensitive sensors CP _s arranged on either side of the rear of the vehicle, and in that the optoelectronic assembly directed towards the rear and formed by at least one light source SL _o and a sensor

photosensitive CP _o .

12 - Optical telemetry system according to claim 1 characterized in that the first optoelectronic assembly formed by two light sources SL _s and two photosensitive sensors CP _s on either side of the front of the vehicle, each of the light sources SL of the follower vehicle is modulated with a specific frequency F, as well as a second optoelectronic set directed towards the rear, formed by two light sources SL _o on either side of the rear of the vehicle and at least one sensor CP photosensitive, each of the SL light sources of the vehicle tracked is modulated with a specific frequency F. 13 - optical telemetry system according to the preceding claim characterized in that the second optoelectronic assembly comprises two sensors

CP photosensitive _o arranged on both sides of the rear of the vehicle.

14 - Optoelectronic assembly for an optical telemetry system according to at least one of the preceding claims, characterized in that it comprises at least one light source SL _s modulated by a frequency signal F _s and at least one photosensitive sensor CP _s and a circuit for measuring the phase difference between the electric signal outputted from said photosensitive sensor _s CP and the modulation signal of the light source _s SL coupled, said system comprising in addition to a calculator for determining the distance as a function of the frequency F and the measured phase shift.

Optoelectronic assembly for an optical telemetry system according to at least one of claims 1 to 8, characterized in that it comprises at least one source

luminous SL _o and at least one photosensitive sensor CP _o , said light source SL _o of the target being modulated by a frequency clock controlled by a phase locked loop controlled by the electrical signal delivered by said photosensitive sensor CP _o .

16 - Method for measuring the distance between two vehicles, characterized in that the front of each vehicle is equipped with a first optoelectronic assembly formed by at least one light source SL _s and at least one sensor

photosensitive CP _s oriented towards the front of the vehicle, and in that the rear of each vehicle is equipped with a second optoelectronic assembly formed by at least one light source SL _o (6) and at least one photosensitive sensor CP _o (5) facing the rear of the vehicle,

• said light sources SL and SL being conventional light sources, the light source SL _s being modulated by a signal of frequency F _s,

Said light source SL _o (6) of the target (4) being

Said first optoelectronic assembly comprising in

Said system further comprising a calculator for

determine the distance as a function of the frequency F _s and the measured phase shift. 17 - Motor vehicle comprising an optical telemetry system for measuring the distance separating it from another vehicle, characterized in that:

• a first end of the vehicle includes a first

an optoelectronic assembly formed by at least one light source SL _s and at least one photosensitive sensor CP _s oriented in the measuring direction of the third vehicle, and

• the opposite end of the vehicle a second set

optoelectronics formed by at least one light source SL _o (6) and at least one photosensitive sensor CP _o (5) oriented towards the measurement direction by a third vehicle,

characterized in that

Said light source SL _o (6) of the target (4) being

modulated by a frequency clock controlled by a phase-locked loop driven by the electrical signal delivered by said photosensitive sensor CP _o · said first optoelectronic assembly comprising

Said system further comprising a calculator for

determine the distance as a function of the frequency F _s and the measured phase shift.

18 - A motor vehicle comprising an optical telemetry system for measuring the distance separating it from another vehicle according to claim 17 characterized in that said first end of the vehicle is the front of the vehicle and the opposite end of the vehicle is the rear of the vehicle, the distance being calculated by the follower vehicle, relative to the distance between the vehicle followed.

19 - Motor vehicle comprising an optical telemetry system for measuring the distance separating it of another vehicle according to the preceding claim characterized in that one of said light sources SL is constituted by at least one of the headlights of the vehicle.

20 - Motor vehicle comprising an optical telemetry system for measuring the distance separating it from another vehicle according to claim 18 characterized in that one of said light sources SL is constituted by at least one of the traffic lights of the vehicle.

21 - A motor vehicle comprising an optical telemetry system for measuring the distance separating it from another vehicle, characterized in that said first end of the vehicle is the rear of the vehicle and the opposite end of the vehicle is the front of the vehicle. vehicle, the distance being calculated by the vehicle followed, with respect to the distance separating it from the follower vehicle.