Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
  • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
  • G01S17/06—Systems determining position data of a target
  • G01S17/08—Systems determining position data of a target for measuring distance only
  • G01S17/32—Systems determining position data of a target for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
  • G01S17/36—Systems determining position data of a target for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated with phase comparison between the received signal and the contemporaneously transmitted signal
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
  • G01S17/88—Lidar systems specially adapted for specific applications
  • G01S17/89—Lidar systems specially adapted for specific applications for mapping or imaging
  • G01S17/894—3D imaging with simultaneous measurement of time-of-flight at a 2D array of receiver pixels, e.g. time-of-flight cameras or flash lidar
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
  • G01S7/4802—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
  • G01S7/483—Details of pulse systems
  • G01S7/486—Receivers
  • G01S7/4868—Controlling received signal intensity or exposure of sensor
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
  • G01S7/483—Details of pulse systems
  • G01S7/486—Receivers
  • G01S7/487—Extracting wanted echo signals, e.g. pulse detection
  • G01S7/4873—Extracting wanted echo signals, e.g. pulse detection by deriving and controlling a threshold value
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06V—IMAGE OR VIDEO RECOGNITION OR UNDERSTANDING
  • G06V20/00—Scenes; Scene-specific elements
  • G06V20/50—Context or environment of the image
  • G06V20/59—Context or environment of the image inside of a vehicle, e.g. relating to seat occupancy, driver state or inner lighting conditions
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06V—IMAGE OR VIDEO RECOGNITION OR UNDERSTANDING
  • G06V2201/00—Indexing scheme relating to image or video recognition or understanding
  • G06V2201/12—Acquisition of 3D measurements of objects
  • G06V2201/121—Acquisition of 3D measurements of objects using special illumination
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06V—IMAGE OR VIDEO RECOGNITION OR UNDERSTANDING
  • G06V40/00—Recognition of biometric, human-related or animal-related patterns in image or video data
  • G06V40/10—Human or animal bodies, e.g. vehicle occupants or pedestrians; Body parts, e.g. hands
  • G06V40/16—Human faces, e.g. facial parts, sketches or expressions
  • G06V40/161—Detection; Localisation; Normalisation

Definitions

• Time of flight sensor and monitoring system comprising such a sensor
• the present invention relates generally to the field of vision and object detection by means of an optical detection system.
• It relates more particularly to a time-of-flight sensor making it possible to reconstruct the three-dimensional mapping of a scene comprising one or more objects.
• Time of flight sensors are known comprising:
• an illumination device comprising a light source emitting a source beam, towards a scene comprising an object capable of reflecting this source beam;
• a detector comprising a matrix of photosensitive pixels and receiving part of the source beam reflected by this reflecting object.
• the light source of the illumination device is either a light-emitting diode (DE) or a laser diode (for example of the VCSEL type).
• DE light-emitting diode
• VCSEL laser diode
• This source generally emits in a narrow band of the infrared domain, around 900 nanometers for example. This means that the source beam is not visible to users present near the sensor (the human eye is only sensitive up to around 800 nm).
• the detector which is of the "matrix” type, is for example formed by a CMOS type camera, the photosensitive pixels of which are sensitive in IR, at least in an absorption band including the narrow emission band.
• the sensor measures the time, therefore called “flight time”, taken by the source beam to go from the source to the object, then by the "reflected" beam) to go from the object to the detector.
• the source beam must be modulated temporally.
• an electronic unit configured to generate a modulation signal and to control the illumination device by means of this modulation signal so that the emitted source beam has a temporally modulated source light power.
• this electronic unit is also configured to: process electrical signals delivered as a function of time by the detector, each electrical signal being representative of a fraction of the source light power reflected by the object towards an associated photosensitive pixel ; and
• a time-of-flight sensor makes it possible to reconstruct a three-dimensional cartography of the scene it observes and to detect shapes there, or even recognize objects (a human body or part of a human body, the eyes of an individual, etc ).
• the electronic time sensor controls the illumination device so that the average light power emitted from the source beam is high enough.
• the present invention provides a time-of-flight sensor having increased security and avoiding the risks of damage by the source beam, in particular the risks of damage to persons.
• a time of flight sensor as defined in the introduction is proposed according to the invention, in which said electronic unit is also configured for, when said object is detected as being at a characteristic distance less than a predetermined threshold distance:
• said electronic unit is also configured to generate a modified modulation signal for controlling said illumination device by means of this modified modulation signal.
• the electronic unit modifies the modulation signal almost instantaneously so that the source beam presents limited light output.
• the predefined maximum value can for example be a danger threshold for the skin or the eyes of an individual.
• this maximum value is defined in the international standard IEC 62471 ("Photobiological safety of lamps and devices using lamps").
• the predetermined threshold distance may in particular depend on this predefined maximum value.
• the characteristic distance of the object detected by the flight time sensor of the invention can be, for example, the average distance or else a weighted distance.
• said characteristic distance is equal to the minimum distance between said illumination device and a particular point of the object reflecting said source beam towards a photosensitive pixel of said detector. In this way, we are sure that as soon as the object (or the individual) enters a particular danger zone, then the average light power is reduced so that no point of said object is illuminated with a source beam. too intense.
• the modified modulation signal controls the extinction of said light source.
• said modulation signal being such that said modulated source light power comprises a periodic succession of light pulses, said modified modulation signal is adjusted so that the source light power comprises a reduced number of light pulses and / or pulses brighter with narrower width and / or lower intensity;
• said electronic unit is further configured to, when said object is then detected as being at another characteristic distance greater than said predetermined threshold distance, generating another modified modulation signal and controlling said illumination device by means of this modulation signal modified so as to increase said source light power beyond a predefined minimum value.
• the time of flight sensor described above advantageously enters into the embodiment of a monitoring system intended to monitor the interior of a passenger compartment of a motor vehicle.
• the invention therefore also provides a monitoring system comprising a time of flight sensor as defined above.
• the reduction of the source light power by the time-of-flight sensor is also conditioned by the recognition of said object as being the head of an occupant (driver, passenger, etc.) of said motor vehicle. .
• FIG. 1 is a schematic view of a vehicle and its passenger compartment which includes a time of flight sensor integrated into a passenger compartment monitoring system;
• FIG. 2 is a schematic view of the time-of-flight sensor of FIG. 1 showing the operating principle of the time-of-flight measurement;
• FIG. 3 shows a human head detected in the passenger compartment of the vehicle in FIG. 1;
• FIG. 5 are graphs showing examples of modulation of the source power emitted by the time-of-flight sensor of FIG. 3.
• FIG 1 there is shown a motor vehicle 1 and its passenger compartment 2, with the front and rear seats.
• a monitoring system 20 is on board inside the passenger compartment 2 of the motor vehicle 1 to allow the acquisition of the cabin environment and its occupants (driver, front and / or rear passenger (s)).
• IMS Interior Monitoring System
• sensor 10 This type of monitoring system is called in English “Interior Monitoring System” or IMS. It comprises a time-of-flight sensor 10 (hereinafter referred to as “sensor 10”) which is generally positioned in the roof modules of the motor vehicle 1 but can also be in front of the driver, near the upright or in the center console.
• the sensor 10 is directly oriented towards the occupants of the car and has a field of vision 17 (see FIG. 1), here so as to cover all the possible positions of the occupants of the motor vehicle 1.
• the senor 10 comprises three elements which we will describe in more detail below: an illumination device 11, a detector 15 and an electronic unit 19.
• the senor 10 faces a scene 3 comprising different “objects” (represented here by geometric shapes) capable of reflecting light, in particular infrared (IR) light.
• objects may for example be the head of the driver or the passenger.
• IR infrared
• the illumination device 1 which can be controlled by the electronic unit 19 (we will see how in the following description), comprises a light source 12 whose light power can be modulated, for example via a current control.
• the illumination device 1 1 emits a source beam 13 (see fig. 2) in the direction of scene 3 comprising the object 4 which will reflect the source beam 13.
• the light source 12 is preferably a source emitting electromagnetic radiation at a wavelength little or not visible to the human eye.
• this light source 12 emits in the infrared range.
• the light source 12 is a light-emitting diode (LED) emitting in the IR, at a wavelength of 940 nm, with an emission width of 60 nm (+/- 30 nm around the central wavelength).
• the diode could emit at a wavelength of 850 nm, or else at any other wavelength in the near infrared range between 800 nm and 1100 nm, or even possibly at a wavelength in the visible spectrum of deep reds, between 700 nm and 800 nm.
• the light source of the device can be a laser diode, in particular of the VCSEL (“Vertical-cavity surface-emitting laser”) type, for example a GaAs / AIGaAs laser diode emitting between 700 nm and 1100 nm.
• VCSEL Vertical-cavity surface-emitting laser
• the illumination device 11 may comprise an optical system placed downstream from the light source 12 for shaping the source beam 13 (see FIG. 2) emitted by the light source 12.
• This optical system can be simply formed of a single lens, or of a doublet.
• a complex optical system can be provided to give particular properties to the source beam 13 (digital aperture, polarization, optical quality, etc.).
• the electronic unit 19 is configured to generate a modulation signal, for example a modulated current signal, intended for the illumination device 11 (see arrow between the unit 19 and the device 11 in FIG. 2).
• a modulation signal for example a modulated current signal
• the light source 12 emits a source light beam 13 which has a source light power Ps which is temporally modulated.
• the modulation signal is here such that during an activation period Ton (also called “integration period”) typically between 1 ps and 10 ms, the illumination device emits a periodic succession of pulses 21 square of power peak Po and of width At between 5 nanoseconds and 500 nanoseconds, at a frequency between 1 and 100 megahertz (MHz).
• Ton also called “integration period”
• the illumination device emits a periodic succession of pulses 21 square of power peak Po and of width At between 5 nanoseconds and 500 nanoseconds, at a frequency between 1 and 100 megahertz (MHz).
• the modulation signal is such that the illumination device 1 1 does not emit a source beam (the current signal received at the input of the illumination device - and therefore from the source luminous - being for example zero current signal).
• the set formed by the Ton activation period and the period Tott inactivation period constitutes a Tacq vesting period.
• the modulation signal could be a sinusoidal signal so that the source light power is modulated sinusoidally as a function of time.
• part 14 of the source beam 13 emitted by the illumination device 11 is reflected by the object 4 present in the scene 3.
• the object 4 To be detected, the object 4 must be in the field of view 17 of the sensor 10 so that the reflected beam 18 is intercepted by the detector 15.
• This detector 15 is a matrix detector (for example “focal plane array”) and comprises a matrix 16 of photosensitive pixels (“pixel array”), in particular at the emission wavelength of the light source 12, c that is to say here in the infrared.
• the detector 15 can also include collection optics, for example a simple lens or a more complex optical system.
• the detector 15 receives part 18 of the source beam 13 (reflected beam 18) reflected by the object 4 in the direction of the detector 15.
• the source beam 13 being temporally modulated, the reflected beam 18 is also temporally modulated (the reflection on the object 4 does not modify this property).
• each photosensitive pixel of the matrix 16 delivers an electrical signal as a function of time which is proportional to the amount of light received by the pixel.
• the electrical signal is representative of the fraction (reflected beam 18) of the light power source P s reflected by the object 4 in the direction of said photosensitive pixel 16A.
• the electronic unit 19 of the sensor 10 is precisely configured to: process these electrical signals delivered as a function of time by the detector 15;
• the electronic unit 19 is further configured for, when the object 4 is detected as being at a characteristic distance Dobj less than a predetermined threshold distance Dmin:
• the senor 10 detects that the object 4 is too close then it decreases the average power of the light source 12 so as to limit the infrared radiation received by the object 4 with the source beam 13.
• the reduction of the source light power is further conditioned by the recognition of said object as being the head 5 of an occupant of the motor vehicle.
• the recognition of the object as being the head of an occupant of the vehicle can for example be carried out by determining that the apparent surface or the volume of said object corresponds to that of a human head.
• the monitoring system includes software processing capable of distinguishing on a three-dimensional representation of the observed scene that the volume detected is a human head.
• FIG. 5 shows an example of the source light power Ps modified by the control of the illumination device 11 with the modified modulation signal generated by the electronic unit 19 after the object 4 has been detected as being at a characteristic distance Dobj less than the distance threshold Dmin.
• this modified light source power P s is such that only one square pulse 21 out of two has been retained (the even order pulses 22 in dotted lines have been deleted), while keeping its level peak Po and its activation period Ton.
• the source light power P s is here halved.
• the characteristic distance Dobj of the object 4 can be taken equal to the minimum distance between the illumination device 1 1 and a particular point of the object 4 reflecting the source beam 14 in the direction d a photosensitive pixel 16A of the detector 15.
• a single particular point of the object 4 (for example the head 5 of the conductor, see FIG. 3) is at a distance less than the threshold distance Dmin for the electronic unit 1 9 modifies the modulation signal in order to limit the light source power Ps.
• the threshold distance Dmin depends on the average light power Ps.
• the average light source power Ps is determined so as to be less than the danger levels defined by standard IEC 62471 for light-emitting diodes and by standard IEC 60825-1 for laser diodes.
• the modified modulation signal generated by the electronic unit 19 controls the extinction of the light source 12 of the illumination device 1 1.
• the light source is completely cut off, by example by canceling the source drive current.
• the electronic unit 19 is further configured for, when the object 4 previously detected as too close to the sensor 10 is then detected as being at another characteristic distance Dobj greater than the predetermined threshold distance Dmin:
• the range of the sensor 10 increases with the average light power of the source beam 13. By increasing the source light power, it is ensured that the object 4 can be detected again when it approaches.
• the other modified modulation signal is preferably identical to the modulation signal generated before the object is detected as being too close.
• the profile of the source light power P s is then that shown in FIG. 4.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Computer Networks & Wireless Communication (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• Electromagnetism (AREA)
• Multimedia (AREA)
• Theoretical Computer Science (AREA)
• Optical Radar Systems And Details Thereof (AREA)

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• 2018
  • 2018-12-14 FR FR1872981A patent/FR3090124B1/fr active Active
• 2019
  • 2019-11-26 WO PCT/EP2019/082602 patent/WO2020120128A1/fr unknown
  • 2019-11-26 US US17/413,766 patent/US20220050202A1/en active Pending
  • 2019-11-26 CN CN201980082468.0A patent/CN113167874A/zh active Pending
  • 2019-11-26 EP EP19809075.5A patent/EP3894886A1/de not_active Withdrawn

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