System for estimating the speed of an aircraft, and an application thereof to detecting obstacles

• US 20070075893A1
• Filed: 05/18/2006
• Published: 04/05/2007
• Est. Priority Date: 05/19/2005
• Status: Active Grant

• Current Assignee: Airbus Helicopters
• Original Assignee: Eurocopter
• Inventors: Petillon, Jean-Paul, Pire, Richard, Filias, Francois Xavier
• Granted Patent: US 7,791,529 B2
• Time in Patent Office: Days
• US Class Current: 342/104
• CPC Class Codes: G01C 21/183 Compensation of inertial measurements, e.g. for temperature effects
• CPC Class Codes: G01S 13/589 measuring the velocity vector
• CPC Class Codes: G01S 13/867 Combination of radar systems with cameras
• CPC Class Codes: G01S 13/882 for altimeters measuring height using barometric means G01C5/06
• CPC Class Codes: G01S 13/89 for mapping or imaging
• CPC Class Codes: G01S 15/588 measuring the velocity vector
• CPC Class Codes: G01S 15/86 Combinations of sonar systems with lidar systems; Combinations of sonar systems with systems not using wave reflection
• CPC Class Codes: G01S 17/86 Combinations of lidar systems with systems other than lidar, radar or sonar, e.g. with direction finders
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 17/933 of aircraft or spacecraft

Abstract

The invention relates to a method of determining an estimated speed of an aircraft relative to ground being overflown by the aircraft, in which use is made of the sum of an acceleration measurement of the aircraft plus a difference value, the difference value being obtained from observation data or signals relating to a region of the ground.

Claims

1. A method of determining at least two components of the estimated speed ({right arrow over ({circumflex over (v)})}) of an aircraft relative to the ground (19), the method comprising the following steps:

successively forming at least two images (z₁(x,y), z₂(x,y)) of a single region of the ground, the images including data relating to the distance between the aircraft and points in the observed region of the ground, and corresponding to measurements delivered by a range finder;

determining a first raw or observed speed as a function of offsets ({right arrow over (d)}) between the images; and

combining the raw or observed speed with inertial measurements of the movement of the aircraft in order to form the estimated speed ({right arrow over ({circumflex over (v)})}).

2. A method according to claim 1, in which the inertial measurements comprise three acceleration components ({right arrow over (γ

)}_m) and three angular speed components ({right arrow over (ω

)}_m) of the aircraft.

3. A method according to claim 1, in which the raw or observed speed measurement is combined by complementary filtering with the inertial measurements of the movement of the aircraft in order to form the estimated speed ({right arrow over ({circumflex over (v)})}), referred to as the hybrid speed.

4. A method according to claim 3, in which an a priori covariance matrix (V) is also determined for the error affecting the raw or observed speed measurement, and in which filtering is performed by a complementary filter (102, 202, 302, 402) having gains (K) that vary and depend on said covariance matrix.

5. A method according to claim 4, in which the complementary filter is a Kalman filter.

6. A method according to claim 1, in which the distance measurements come from a scanning range finder such as a lidar, a radar, a sonar, or an SAR;

or else from a “

snapshot”

range finder.

7. A method according to claim 6, in which the distance measurements are obtained by scanning the region of the ground.

8. A method according to claim 1, in which the images comprise light intensity data (I) of points of the observed region of the ground as delivered by at least one camera, and in which a second raw or observed speed is determined as a function of offsets between said images.

9. A method according to claim 1, in which the means for determining the raw or observed speed ({right arrow over (v)}_R) from the images implement a differential method.

10. A method according to claim 1, in which the means for determining the raw or observed speed ({right arrow over (v)}_R) from the images implement a correlation method, a method based on energy, a method using parameterized models, or a combination of said methods.

11. A method according to claim 1, in which measurements of the airspeed of the aircraft (i.e. its speed relative to air) are also combined with the inertial, distance, and where appropriate light intensity measurements.

12. A method according to claim 1, in which heading and/or magnetic field measurements are also combined with the inertial, distance, and where appropriate light intensity measurements.

13. A method according to claim 1, in which altitude and/or barometric pressure measurements are also combined with the inertial, distance, and where appropriate light intensity measurements.

14. A system (18) for determining an estimated speed ({right arrow over ({circumflex over (v)})}) of an aircraft (25) including an inertial measurement unit (23) delivering signals or data relating to measured movement of the aircraft, the system further comprising:

means (11) for measuring distances between the aircraft and points in a region of the ground (19);

means (16, 116, 216, 316, 416) for determining an observed or raw speed measurement ({right arrow over (v)}_R) as a function of the distance signals or data delivered by the distance measurement means (11); and

hybridization means (24) for combining the inertial measurements and the observed speed ({right arrow over (v)}_R) and for delivering the estimated or “

hybrid”

speed ({right arrow over ({circumflex over (v)})}).

15. A system according to claim 14, in which the means (16, 116, 216, 316, 416) for determining an observed or raw speed measurement produce a speed difference ({right arrow over ({circumflex over (v)})}−

{right arrow over (v)}_R), and in which the hybridization means (24) include filter means (13) for filtering said speed difference and the inertial measurements.

16. A system according to claim 15, in which the filter means (13) present gain (K) that is variable as a function of the covariances (V) of the errors affecting the distance measurements and also as a function of the covariances (U) of the errors affecting the inertial measurements.

17. A system according to claim 14, in which the observed speed is determined from an offset ({right arrow over (d)}) between two successive series of distance measurements, and from the time interval (τ

) between said two series of observations of a single region of the ground.

18. A system according to claim 14, in which the measurement means (11) comprise a scanning remote detection sensor such as a radar, a lidar, a sonar, or an SAR;

or else a “

snapshot”

range finder which delivers a plurality of measurements or echoes in three dimensions from points on the ground.

19. A system according to claim 14, further comprising a barometric altimeter, a magnetometer (92), and/or an airspeed sensor (93), together with hybridization means for combining the measurements delivered by these sensors with the inertial and distance measurements.

20. A system according to claim 14, further including at least one passive observation sensor such as an infrared camera, and means for determining a second observed speed from images delivered by said sensor and from the distance measurements, in order to mitigate stages during which it is not possible to estimate raw or observed speed from distance measurements only, as for example when overflying flat terrain.

22. A system of detecting obstacles for a rotary wing aircraft that includes a system for estimating at least two components of the travel speed of the aircraft in accordance with claim 14.

23. A system according to claim 22, that does not make use of and/or that is independent of a satellite positioning system.

21. A method of detecting obstacles while on board an aircraft, in particular while on board a rotary wing aircraft, the method comprising the following operations:

extracting at least one observed or raw speed ({right arrow over (v)}_R) for the aircraft from at least one sequence of images or sets of echoes of a region or relief overflown by the aircraft, the images or sets of echoes being delivered by an observation sensor (11) installed on board the aircraft, each image or set of echoes comprising information including relative three-dimensional positions for the aircraft and a plurality of points of the relief being overflown;

hybridizing the observed speed with the speed delivered by an on-board inertial sensor; and

detecting obstacles from the echoes and from the speed obtained by hybridizing.