• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
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  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    The invention relates to a distance measuring system of an obstacle (14), in which an optical flux is measured radially in rotation on a circle (12) in a plane intersecting the obstacle; and the distance of the obstacle is determined according to the amplitude of the optical flux, the radius of the circle, and the speed of rotation.
    公开号:FR3057347A1
    申请号:FR1659663
    申请日:2016-10-06
    公开日:2018-04-13
    发明作者:Stephane Marie Vincent VIOLLET；Fabien Thierry Alain COLONNIER；Erik VANHOUTTE
    申请人:Aix Marseille Universite；Centre National de la Recherche Scientifique CNRS；
    IPC主号:
    专利说明:

    Holder (s): UNIVERSITY OF AIX-MARSEILLE Public establishment, NATIONAL CENTER FOR SCIENTIFIC RESEARCH.
    Extension request (s)
    Agent (s): OMNI PAT Société anonyme.
    SYSTEM FOR MEASURING THE DISTANCE OF AN OPTICAL FLOW OBSTACLE.
    (6 /) The invention relates to a system for measuring the distance of an obstacle (14), in which an optical flux is measured radially in rotation on a circle (12) in a plane intersecting the obstacle; and the distance from the obstacle is determined as a function of the amplitude of the optical flux, the radius of the circle, and the speed of rotation.
    FR 3 057 347 - A1
    Obstacle distance measurement system
    BY OPTICAL FLOW
    Technical area
    The invention relates to obstacle detection systems using optical fluxes, in particular for aircraft.
    Background
    Optical flows are often considered in anti-collision systems for drones. The articles by Laurent Muratet et al., “A Contribution to Vision-Based Autonomous Helicopter Flight in Urban Environments” (Robotics and Autonomous Systems, Volume 50, Issue 4, Pages 195-209, 31 March 2005), and Simon Zingg and al., “MAV Navigation through Indoor Corridors Using Optical Flow” (ICRA 2010), for example, propose to guide a drone between buildings by equalizing the optical fluxes of the lateral bands of an image taken by a camera oriented in the direction of displacement. The optical fluxes of the image are thus used in a qualitative or differential manner, without calculating an absolute speed or distance.
    FIG. 1A illustrates an image taken by a front camera during the movement of a drone between buildings, according to a configuration proposed in these articles. A nearby building, visible on the right band of the image, causes a higher optical flux (represented by an arrow to the right) than a distant building appearing in the left band of the image. The punctual observation of the optical fluxes of this image tends to indicate that we must turn to the left to decrease the optical flux to the right.
    FIG. 1B illustrates an optical flux obtained when the camera faces a flat frontal obstacle (a facade) which occupies the entire field of vision. The optical flux increases radially from the center, the flux being zero in the central zone. Such a flux field can only be exploited to avoid a collision if the image of the obstacle extends beyond the central zone enough for the optical flux to be measurable. If the obstacle is small and is on the axis of movement, it could remain undetectable.
    To determine a distance from an optical flux, it is known that the translation components must be used, while the raw values of optical flux supplied by the sensors include rotation components which must be compensated. The components of rotation to be compensated for can be measured by a gyroscopic system mounted in the aircraft.
    Thus, optical fluxes are generally not used to measure distances quantitatively. In some vehicles, however, optical fluxes are used to provide speed quantitatively, such as the ground speed of an aircraft. To calculate the speed, the system needs the distance to the object under observation (e.g. flight altitude), a value that is known to or supplied to the system by another sensor (e.g. altimeter).
    summary
    To measure the distance of an obstacle according to the invention, provision may be made to measure an optical flux radially in rotation on a circle in a plane cutting through the obstacle; and determine the distance from the obstacle based on the magnitude of the optical flux, the radius of the circle, and the speed of rotation.
    For this, it is possible to provide a device for measuring the distance of an obstacle, comprising a rotary element configured to rotate at a determinable speed of rotation; and an optical flow sensor configured to measure an optical flow at an eccentric point on the rotating member.
    The optical flux sensor can be configured to measure the optical flux radially or axially.
    The device may include an optical flow sensor operating circuit configured to determine the distance of the obstacle from a maximum of optical flow measured during a revolution of the rotary element, of the eccentricity of the measuring point, and the rotation speed.
    The operating circuit can be configured to determine the orientation of the obstacle from the angular position of the rotary element for which the maximum optical flux is measured.
    The optical flow sensor can be a local motion sensor. The optical flow sensor can then comprise an optical system mounted eccentrically on the rotary element, a remote photosensitive sensor close to the center of rotation of the rotary element, and optical fibers connecting the optical system to the photosensitive sensor.
    The values of the speed of rotation and the eccentricity can be chosen to make negligible other components of speed occurring during the use of the device.
    A helicopter rotor blade can be provided with a measuring device of the aforementioned type, the optical flux sensor being configured to measure the optical flux at the distal end of the blade.
    Brief description of the drawings
    Embodiments will be set out in the following description, given without limitation in relation to the attached figures, among which:
    • Figures IA and IB, previously described, represent images used to exploit an optical flux;
    FIG. 2 illustrates a helicopter in top view, comprising optical flux sensors at the tip of the blade, according to an embodiment of a distance measurement system based on optical fluxes;
    • Figure 3 is a graph illustrating the evolution of the optical flux provided by the system of Figure 2 in the presence of a flat vertical obstacle as a function of the angular position of the blades;
    • Figure 4 illustrates an example of a local motion sensor usable in the system of Figure 2; and • Figure 5 illustrates a variant of local motion sensor usable in the system of Figure 2.
    Description of embodiments
    An optical flux is inseparable from the presence of movement in the image observed by the sensor. The measurements are all the better when the speed is high and the area of interest is far from the axis of movement. Until now, the measurement of optical flux in an aircraft has been based on the movement of the aircraft alone. However, some aircraft, such as helicopters, can have a slow or hovering flight, making it difficult to detect obstacles near the blades, such as a rock wall, with known techniques based on optical fluxes.
    Here, we propose to animate the optical flow sensor with a permanent movement relative to the vehicle, according to a configuration offering an exploitable optical flow even if the vehicle is stationary. More specifically, it is proposed to measure the optical flux in rotation on a circle, for example at the end of the rotor blades of a helicopter.
    Rotations are in principle unusable in an optical flux, because they introduce components independent of the observation distance. This is only true in reality for "pure" rotations, that is, when the flow sensor is on the axis of rotation. The fact of offsetting the flux sensor relative to the axis of rotation produces a tangential speed which, in turn, introduces an exploitable component of translation into the optical flux.
    FIG. 2 illustrates an example of implementation of this system in a helicopter. The helicopter, seen from above, comprises, for example, a rotor with three blades 10. At the distal end of each blade is mounted an optical flow sensor 12, oriented radially outwards. The axis of observation of each sensor, illustrated by a dotted arrow, is radial.
    The rotor rotates at an angular speed Ω, causing a tangential speed Vt of the sensors, equal to QR, where R is the distance of the sensors from the center of rotation. Each sensor produces a total flux, expressed in radians per second:
    CÛtot - ®rot “b Otrans
    Where o r ot is a component of rotation equal to the angular speed Ω of the rotor and o t rans is a component of translation which depends on the tangential speed Vt = QR. For any angular position Θ of a blade 10, the translation component is expressed by:
    Otrans = Vt / D = QR / D
    Where D is the distance between the end of the blade and the closest object in the extension of the blade (in the optical axis of the corresponding flow sensor 12).
    So
    Otot = Ω (1 + R / D)
    This allows the distance to be expressed as a function of the total flow measured:
    D = RΩ / (ωtot - Ω)
    In the case of a helicopter, the angular speed Ω is substantially constant and known, of the order of 40 radians per second for a rotor with three blades and a diameter of 10 m. The propulsion power is adjusted by modifying the pitch of the blades. The length of the blades being of the order of 5 m, the tangential speed Vt is significant, of the order of 200 m / s. This speed is so high that most of the other movements, notably occurring during a helicopter flight over obstacles, have a negligible influence on the optical flux, so that their compensation is superfluous.
    The cruising speed of a helicopter, up to 100 m / s, could have an influence on the measured optical flux. However, such a cruising speed is only used in open ground, in principle requiring no obstacle monitoring.
    The application of the measurement principle to a helicopter with counter-rotating rotors eliminates a possible problem related to flight speed. In fact, the blades of the two rotors sweep the ground in opposite directions, so that the flight speed is added to the ones and subtracts from the others for a given angular position Θ. Thus, the flight speed disappears in the calculation of the average of the flux produced by a blade of the first rotor and of the flux produced by a blade of the second rotor at the same angular position Θ.
    In any case, the helicopter's flight speed is generally measured. This measurement of the flight speed can, if necessary, be used to compensate for the optical flux measurements by knowing the angular positions of the optical flux measurements.
    The pitch of the blades theoretically has an influence on the flow measurement, since the modification of the pitch modifies the inclination of the flow sensor relative to its axis of displacement. However, since the pitch is adjusted within a range of about 5 ° amplitude, the influence is only 0.4% (1 - cos 5 °), so that compensation is also superfluous.
    As the blades 10 rotate, the flow sensors 12 probe obstacles around the helicopter in line with the plane of the blades. Front obstacles, located on the helicopter's axis of movement, even small, are as accurately detectable as other obstacles. The presence of a nearby obstacle is characterized by a local maximum of the optical flux measured by a given sensor 12, and the orientation of the obstacle relative to the longitudinal axis of the helicopter is provided by the angular position of the blade in the plane containing the blades at which the local maximum is measured. The angular position of the blade, if it is not provided by a sensor present in the helicopter, can be deduced from the angular speed of the rotor and from a mark on the helicopter which is located in the swept field by flow sensors, such as the tail fin or the anti-torque rotor.
    FIG. 2 also represents a particular obstacle, namely a vertical wall 14, such as a cliff or a building facade. In some helicopter operations, it is desirable to get as close as possible to the wall. However, it is difficult to assess the distance of a wall from the ends of the blades, and in particular to maintain a sufficient distance while maneuvering the helicopter. It is also difficult to recognize the nearest point on a long wall.
    The fact that the flow sensors 12 have a circular trajectory is useful in this situation. Indeed, the translation flow, instead of being almost constant as in the case of a rectilinear trajectory, is expressed by:
    cos 2 (0 - θ 0 ) ^ rans Vt ^ (1 _ cos (0 _ θ θ) ) +
    Where Θ is the angle of the blade 10 considered relative to the longitudinal axis of the helicopter, θο is the angle of the blade relative to the longitudinal axis of the helicopter when its end is closest to the wall (for example the right blade in Figure 2), and Dmin is the distance measured for θ = θ 0 (shortest distance).
    FIG. 3 is a graph illustrating the evolution of the translational optical flux o t rans as a function of the angular position of a blade, for R = 5 m, D m i n = 10 m, and Vt = 200 m / s . The translation flow has a local maximum marked for θ = θ 0 . Thus, the evaluation of the distance to a wall and the determination of the orientation thereof follow the same methodology as for detecting an isolated obstacle, namely the search for a local maximum among the measurement samples, and the determination of the blade angle at which this local maximum is noted.
    The optical flux measurements being based on the contrasts of the objects observed, dedicated optical flux sensors are proposed, significantly simpler than cameras operated by an image processing algorithm. Such sensors are called LMS ("Local Motion Sensor"), or local motion sensor, and are inspired by the vision of insects. Such sensors are also well suited for use at high speeds, for example of the order of 200 m / s at the ends of the blades of a helicopter. Indeed, their simplicity implies low computing resources, which makes it possible to provide the measurements at a rate compatible with the high speed of movement. They are also light, so they are little stressed when subjected to the centrifugal forces encountered at the end of a helicopter blade. Sensors
    LMS are described, for example, by Fabien Expert et al., In the article “Outdoor field performances of insect-based visual motion sensors” (Journal of Field Robotics 2011).
    FIG. 4 schematically represents an example of an elementary LMS sensor directed towards the wall 14, illustrated here by a succession of contrasts. The sensor comprises a pair of photodiodes 40 aligned in the direction of the displacement to be measured, here according to the tangential speed Vt. A lens 42 is arranged so that the two photodiodes observe the scene along two axes spaced apart by a small angle Δφ, of the order of 1 °.
    In short, the optical flux is determined as the ratio between the angular deviation Δφ and the time elapsed between the detections of the same pattern contrasted by the two photodiodes.
    The signals coming from the two photodiodes are normally identical but shifted in time. They undergo bandpass filtering and then a correlation at 44 which makes it possible to measure the time difference between the two signals. The optical flux is the inverse of this time difference multiplied by the angular deviation. Finally, the distance D is obtained at 46 from the radius R and the angular speed Ω, known parameters.
    To improve the measurements, the LMS sensor can be configured so that each photodiode has a substantially Gaussian angular sensitivity characterized by the half-height angle called Δρ. This Gaussian angular sensitivity can be obtained, for example, by slightly defocusing the lens 42. This in particular makes it possible to perform low-pass spatial filtering limiting false measurements of optical flux. This configuration is described, for example, in [F. L. Roubieu, F. Expert, M. Boyron, B. Fuchslock, S. Viollet, F. Ruffier (2011) “A novel 1-gram insect based device measuring visual motion along 5 optical directions”, IEEE Sensors 2011 conference, Limerick , Ireland, pp. 687-690]. This technique tends to make the LMS sensor "myopic".
    In other words, the sensor does not work beyond a certain distance. An LMS sensor used in helicopter blades can be designed to have a range of 20 to 30 m, which is sufficient for many situations, in particular hovering near vertical walls.
    More efficient variants of the LMS sensor include several pairs of aligned photodiodes, often three pairs.
    All of the elements in FIG. 4 could be mounted at the end of each blade of the helicopter. In certain applications, this assembly could however be too heavy or bulky taking into account the dimensions of the blade, in particular if it is a blade of a drone rotor.
    FIG. 5 illustrates a variant of the sensor of FIG. 4 which can be installed in small blades. The sensor of Figure 4 is split into two parts. Only the optical system 42 of the sensor is mounted at the distal end of the blade 10, for example in a housing provided for this purpose in the blade. Photodiodes 40, which can be mounted with their operating circuits on a more bulky module, are offset at the proximal end of the blade, near the center of the rotor. A bundle of optical fibers 50 connects the optical system 42 to the photodiodes 40. This bundle 50 can be embedded in the mass of the blade during the molding of the blade or slid into a channel previously arranged in the blade. The beam 50 may include numerous individual optical fibers which provide independent guidance of the fluxes intended for the two photodiodes.
    A measurement system thus arranged in the blades of the main rotor of a helicopter makes it possible to detect obstacles in the plane containing the blades, and beyond this plane according to the angle of vision of the sensors used. If we also want to detect obstacles in a vertical plane, we could apply the measurement system to the helicopter's anti-torque rotor, if it is not in a fenestron.
    Also, for automatic terrain monitoring and for landing problems where the measurement of the distance between an aircraft and the mobile landing platform is desirable, it is possible to orient the optical flow sensors perpendicular to the plane containing the blades, that is to say axially. In this case, the rotation component œ ro t linked to the rotation of the rotor disappears from the raw measurements provided by the optical flux sensors, but it is then possible to take account of variations in the pitch of the blades.
    Many variants and modifications of the embodiments described here will appear to those skilled in the art. Although the distance measurement system has been described primarily in connection with a helicopter, it can be used in any vehicle, whether or not it has blades. If the vehicle does not originally have blades, a rotating element, such as a disc or a ring, can be mounted on the vehicle for this purpose, in a plane that one wishes to monitor.
    权利要求:
    Claims (10)
    [1" id="c-fr-0001]
    Claims
    1. Device for measuring the distance of an obstacle, comprising:
    • a rotary element (10) configured to rotate at a determinable speed of rotation; and
    5 "an optical flow sensor (12) configured to measure an optical flow at an eccentric point of the rotating element.
    [2" id="c-fr-0002]
    2. Device according to claim 1, in which the optical flow sensor is configured to measure the optical flow radially.
    [3" id="c-fr-0003]
    3. Device according to claim 1, in which the optical flow sensor is configured to measure the optical flow axially.
    [4" id="c-fr-0004]
    4. Device according to claim 2, comprising an operating circuit (44, 46) of the optical flux sensor configured to determine the distance (D) of the obstacle from a maximum of measured optical flux (ω | 0 | ) during a revolution of the rotary element, the eccentricity of the measuring point (R), and the speed of
    15 rotation (Ω).
    [5" id="c-fr-0005]
    5. Device according to claim 4, in which the operating circuit is configured to determine the orientation of the obstacle from the angular position of the rotary element for which the maximum optical flux is measured.
    [6" id="c-fr-0006]
    6. Device according to claim 1, in which the optical flux sensor is a local motion sensor.
    [7" id="c-fr-0007]
    7. Device according to claim 6, in which the optical flow sensor comprises:
    • an optical system (42) mounted eccentrically on the rotary element, • a photosensitive sensor (40) offset near the center of rotation of
    25 the rotary element, and • optical fibers (50) connecting the optical system to the photosensitive sensor.
    [8" id="c-fr-0008]
    8. Device according to claim 1, in which the values of the speed of rotation and of the eccentricity are capable of rendering negligible other speed components occurring during the use of the device.
    [9" id="c-fr-0009]
    9. Helicopter rotor blade comprising a measuring device according to claim 8, the optical flux sensor (12) being configured to measure the optical flux at the distal end of the blade.
    [10" id="c-fr-0010]
    10. Method for measuring the distance of an obstacle, comprising the following steps:
    • measure an optical flux radially in rotation on a circle in a plane cutting the obstacle; and
    10 · determine the distance of the obstacle according to the amplitude of the optical flux, the radius of the circle, and the speed of rotation.
    1/2 ϊ->
    vt
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    法律状态:
    2017-10-24| PLFP| Fee payment|Year of fee payment: 2 |
    2018-04-13| PLSC| Publication of the preliminary search report|Effective date: 20180413 |
    2018-10-22| PLFP| Fee payment|Year of fee payment: 3 |
    2019-10-28| PLFP| Fee payment|Year of fee payment: 4 |
    2020-10-21| PLFP| Fee payment|Year of fee payment: 5 |
    2021-10-20| PLFP| Fee payment|Year of fee payment: 6 |
    优先权:
    申请号 | 申请日 | 专利标题
    FR1659663A|FR3057347B1|2016-10-06|2016-10-06|SYSTEM FOR MEASURING THE DISTANCE OF AN OBSTACLE BY OPTICAL FLOW|
    FR1659663|2016-10-06|FR1659663A| FR3057347B1|2016-10-06|2016-10-06|SYSTEM FOR MEASURING THE DISTANCE OF AN OBSTACLE BY OPTICAL FLOW|
    EP17787237.1A| EP3523602B1|2016-10-06|2017-10-05|System for measuring the distance of an obstacle by optical flow|
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    ZA2019/02532A| ZA201902532B|2016-10-06|2019-04-23|System for measuring the distance of an obstacle by optical flow|
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