IL199629A - Method for the autonomous guidance of an aircraft and corresponding aircraft - Google Patents

Abstract

The invention relates to a method for guiding an aircraft (1) in an environment (2), the aircraft (1) including at least one sensor (3) with an environment-observation optical field (4), the environment (2) being displayed in the field of the sensor (3) during the movement of the aircraft relative to a fixed point (5) at the centre of the field, characterised in that it comprises the step of: determining at least two magnitudes related to the display of the environment, one magnitude being located on one side of the fixed point (5) and the other being located on the other side of the fixed point (5); determining a deviation between the two magnitudes; automatically guiding the aircraft in the environment, the guiding direction depending on said deviation. The invention also relates to an aircraft for implementing said method.

Description

METHOD FOR THE AUTONOMOUS GUIDANCE OF AN AIRCRAFT AND CORRESPONDING AIRCRAFT ap o'u '^Di ο·ϋ '"7D *7y ινηηιυικ miDn1? nu'y Eitan-Mehulal Law Group Advocates-Patent Attorneys P-11160-IL IN THE MATTER OF a Patent Application in Israel corresponding to PCT/EP2008/050055 fded on January 04, 2008 in the name of SAGEM DEFENSE SECURITE I, Aymeric VIENNE C/O CABINET REGIMBEAU, do solemnly and sincerely declare that I am conversant with the English and French languages and am a competent translator thereof, and that to the best of my knowledge and belief the following is a true and correct translation of the International Patent Application filed under No. PCT/ EP2008/050055 in the name of SAGEM DEFENSE SECURITE; For : METHOD FOR THE AUTONOMUS GUIDANCE OF AN AIRCRAFT AND CORRESPONDING AIRCRAFT Date : June 24, 2009 1 METHOD FOR THE AUTONOMOUS GUIDANCE OF AN AIRCRAFT AND CORRESPONDING AIRCRAFT GENERAL TECHNICAL FIELD The present invention relates to a method for guiding an aircraft in an environment, the aircraft including at least one sensor with an environment-observation optical field, the environment being continuously displayed in the field of the sensor during the movement of the aircraft relative to a fixed point at the centre of the field.

The invention also relates to an aircraft applying the method. 2 STATE OF THE ART Many techniques are known for autonomous guidance of an aircraft in an environment.

Certain techniques from the state of the art have the goal of guiding an aircraft, such as for example a drone, moving at low altitude in an environment including obstacles, the aircraft being capable of avoiding the obstacles autonomously.

The aforementioned techniques generally use an active sensor - such as for example a laser, radar, or sonar - or GPS (Global Position System) type sensor.

However they have drawbacks .

The techniques using active sensors are complex, generally require a priori knowledge of the environment and are expensive.

Techniques using GPS type sensors require a mapping of the environment, a mapping which has to be prepared before the mission for guiding the aircraft. They thereby also require a priori knowledge of the environment. GPS type sensors are moreover heavy to load onboard an aircraft . 3 PRESENTATION OF THE INVENTION The invention proposes to find a remedy to at least one of these drawbacks.

For this purpose, according to the invention, a method for guiding an aircraft in an environment is proposed, the aircraft including at lest one sensor having an environment-observation optical field, the environment being continuously displayed in the field of the sensor, during the movement of the aircraft, relatively to a fixed point at the centre of the field, characterized in that it includes a step of: - determining at least two quantities related to the continuous display of the environment, one quantity being located on one side of the fixed point, and another quantity being located on another side of the fixed poin ; - determining a deviation between both quantities; - automatically guiding the aircraft in the environment, a guiding direction depending on said deviation. 4 The invention is advantageously completed by the following characteristics, either taken alone or in any of their technically possible combinations: - the method includes a step consisting of determining two quantities related to the horizontal display of the environment on a horizontal axis in the field and/or two quantities related to the vertical display of the movement on a vertical axis in the field, the automatic guidance direction along a direction parallel to the horizontal axis and/or along a direction parallel to the vertical axis, depending on the deviation between both quantities on each axis; - the automatic guidance of the aircraft along at least one direction is carried out along a direction tending to cancel out the deviation; - a normal automatic guidance mode of the aircraft, along at least one direction of tolerance, involves a servocontrol around a deviation less than or equal to a predetermined non-zero threshold, automatic guidance of the aircraft along said direction of tolerance tending to again find a deviation less than or equal to said predetermined threshold, being triggered when the deviation is above said threshold; - the direction along which the deviation is involved is the vertical direction; 5 - a specific automatic guidance mode for the aircraft along said direction tolerance is triggered in order to maintain a deviation equal to said predetermined threshold; - the width of the field is adjusted according to the quantities ; - the angular accuracy of each pixel is adjusted according to the quantities; - the aircraft includes two sensors, the steps of determining at least two quantities related to the continuous display of the environment and determining the deviation being carrying out in the field of each sensor, the guidance being carried out depending on the difference of the deviations of the sensors; - the intensity of the guidance depends on the absolute value or the average of the quantities; - when the deviation of the quantities is significant, the guidance intensity Imp is of the form Imp = Mass * V (aircraft) * (β) wherein Mass is the mass of the aircraft, V (aircraft) is the velocity of the aircraft, and wherein Ρ{β) is a function of β, where β is the angle between a line of 6 obstacles to be avoided and the direction of movement of the aircraft; - the quantity related to the continuous display is the actual display or an average value of a plurality of dis lays ; - the quantity related to the display is the time derivative of the display.

The invention also relates to an aircraft applying the aforementioned method.

The invention has many advantages.

With it, it is possible to use a so-called "passive" sensor, i.e. an optical sensor of the video camera type.

Also it thus allows a simpler and less expensive guidance method.

The invention does not require a priori knowledge of the environment. The invention neither requires mapping of the environment.

With the invention, it is possible to give low altitude flying aircrafts, and in the vicinity of obstacles, a capability of being guided autonomously. This capability is obtained by using the observations of at least one imaging sensor onboard the aircraft, the 7 sensor being located in the axis of progression of the aircraft .

The invention in particular utilizes an observed display deviation, for example on the right and on the left of the centre of the field of the sensor. This piece of information is used in order to determine as early as possible the direction of the guidance maneuver to be carried out. It thus utilizes the information of nascent displays in the image in order to detect as early as possible obstacles, estimate their proximity (time, distance) and elaborate avoidance maneuvers upstream.

The guidance order is directly calculated from measured displays . There is no need to reconstruct a 3D environment, which means that the method is applied in a robust way and in real time on the aircraft.

The goal of the invention is not to react to emergency situations. The invention is only applied on a narrow field around the central axis of progression of the aircraft. The present resolution of optical sensors allows with certain robustness, the detection of objects and their display in proximity to the central axis.

The closer the observation is to the centre, the better is the guidance quality, because there is then: - earliness of detection, 8 - geographical consistency of the information, providing a good estimation of the presentation of the obstacle.

The invention may be completed by another guiding method, for a capability of monitoring obstacles with two levels, i.e. long term guidance and short term guidance. For this purpose, one has: - narrow field monitoring {object of the invention) for detecting obstacles as earliest as possible and carrying out long term guidance, - wide field monitoring in order to complete the observations of close obstacles: a different sensor of a radio probe type, may account for the presence of obstacles occurring at strong misalignments for short term guidance.

PRESENTATION OF THE FIGURES Other characteristics, objects and advantages of the invention will become apparent from the description which follows, which is purely illustrative and non-limiting and which should be read with reference to the appended drawings wherein: - Fig. 1 schematically illustrates a profile view of an aircraft in an environment; 9 - Fig. 2 schematically illustrates a field of a sensor of an aircraft; - Figs. 3 and 4 schematically illustrate a top view of an aircraft in an environment; - Figs. 5A and 5B schematically illustrate a field of a sensor with points being displayed in detection bands, Fig. 5A illustrating the lateral guidance and Fig. 5B the guidance along two axes; - Fig. 6 schematically illustrates a top view of a maneuver for avoiding an obstacle; - Fig. 7 schematically illustrates means for applying the method according to the invention; - Figs. 8 and 9 schematically illustrate fields of a sensor; - Fig. 10 schematically illustrates a profile view of an aircraft including a pivotally mounted sensor, the pivoting may be required for aligning the sensor with the level flight velocity vector or during a landing maneuver; and - Fig. 11 schematically illustrates an aircraft including two sensors . 10 In the whole of the figures, similar elements bear identical numerical references.

DETAILED DESCRIPTION It is specified here that in the present description, the invention makes use of the assumption that the environment is static or that elements belonging to the environment move very slowly relatively to the movement of the aircraft in the environment.

As this is shown in Figs. 1 and 2, the invention relates to a method for guiding an aircraft 1 in an environment 2. The aircraft 1 includes at least one sensor 3 having an environment -observation optical field 4.

The description mainly applies to information on a single axis, the horizontal axis X in field 4. The principle however applies on both axes: the horizontal axis X and the vertical axis Y.

The environment 2 is being continuously displayed in the field 4 of the sensor 3 during the movement of the aircraft 1 relatively to a fixed point 5 at the centre of the field 4.

As this is shown in Fig. 3, the field 4 of the sensor 3 onboard the aircraft 1 moving at velocity V, and around the centre of the image corresponding to the fixed 11 point 5, observed patterns Ml, M2 and M3 are continuously displayed laterally 6i (i=l to 3) in a plane P perpendicular to V, which depends on the misalignment i {i=l to 3) and on their distance to the aircraft (Di (i=l to 3) : V ά sin ai with i = 1 to 3 Di It is specified here that what is called a "pattern" is any shape originating from the processing of images, such as for example a point, a segment or any other object.

Thus, at least two quantities 6l and 62 are determined, related to the display of the environment. The quantity δΐ is located on one side of the fixed points, and the other point δ2 is located on the other side of the fixed point 5.

A deviation Δ between both quantities is then determined and the aircraft is automatically guided in the environment, one guidance direction depending on said deviation.

In the example of Fig. 4, both determined quantities are the displays 6l and 62 on a horizontal axis X in the field 4. The automatic guidance direction along a direction parallel to the horizontal axis X depends on the deviation or difference Δ = 6l -δ2 between both displays on the axis X. 12 In order to avoid an obstacle materialized by a pattern Mi, the automatic guidance of the aircraft along said direction is carried out along a direction tending to cancel out the deviation Δ. In other words, the deviation between both displays gives a resulting display and the automatic guidance along the horizontal axis is carried out in the direction opposite to the resulting observed display.

The use of the invention is optimum with the significant displays being detected as early as possible, i.e. in the vicinity of the centre 5 of the field 4 of the sensor.

As shown in Fig. 4, in the case of an aircraft 1 flying over a low altitude relief, the assumption may be made that the obstacles are distributed in a relatively continuous way over a relief line 6.

The display will therefore be a continuous function changing rather slowly. Filtering may take into account this behavior. Further, a computation performed on a restrictive number of patterns {corresponding to Ml and M2 for example) which are displayed may allow an estimation of the proximity of the relief line 6.

As shown in Figs. 5, utilization of the quantities is optimum on typically two bands 41 and 42 or 43 and 44. As shown in. Fig. 5A, determination of the quantities may be carried out on both bands 41 and 42 of the field 4, on either side and close to the fixed point 5 of the field 13 4. 100 or 150 mrd may be typically assumed between the bands 41 and 42. It is in the bands 41 and 42 that the continuously displayed patterns corresponding to Ml -MS for example will be detected.

Of course, the bands 41 and 42 may be more or less extended along the axis X and along the axis Y. The bands 41 and 42 are relatively close to the fixed point 5 in order to obtain good anticipation of the guiding maneuvers to be carried out, but relatively away from each other in order to allow sufficient detection of the continuous displays of the points.

It is recalled that, as shown in Fig. 2, the vertical axis Y may also be taken into account.

In this case, the determination of the quantities may also be carried out on two bands 43 and 44 of the field 4, on either side and close to the fixed point 5 of the field 4 (typically 100 or 150 mrd between the bands 43 and 44), but on the vertical axis Y. It is also in the bands 43 and 44 that the continuously displayed patterns will be detected. As earlier, for the bands 41 and 42, the bands 43 or 44 may be more or less extended along the X axis or along the Y axis.

Of course, with the patterns corresponding to M6, M7 and M8 and located both in the bands 43 or 44 and 41 and 42 it is possible to obtain information along both axes X and Y. 14 The following Table 1 gives the relationship between the velocity of the aircraft, the distance to the object, the remaining time for the guidance maneuver, the misalignment of the observation, the geometrical display and the display in the sensor. The numerical examples of the table assume a sensor for which the angular resolution of the pixel' has the value 0.1 mrd. The observation field is then 100 mrd for a 1,000 x 1,000 pixel matrix.

Table 1 With reference to Fig. 5A, a specific example of an application of the method according to the invention is described below, in which there are several patterns being continuously displayed in the field .

For the patterns being displayed, corresponding to M1-M5, the average display is calculated on the left of the fixed point 5 of the image, i.e. the average display δΐ34 for the patterns Ml, M3 and M4 , and the average display δ25 on the right, i.e. the average display for the patterns M2 and M5. 15 Both quantities 6134 and 825 related to the continuous display of the environment are thereby determined, the quantity δ25 being located on one side (on the right} of the fixed point 5 and another quantity δι34 being located on the other side (on the left) of the fixed point 5. From both of these quantities, it is possible to infer: - their absolute value or the average of both quantities, giving an estimation of the distance of the obstacle line 6 to the aircraft 1. The intensity of the guidance maneuver to be applied will depend on this estimation; and - their deviation Δ or difference - giving an estimation of the tilt β of the obstacle line 6. This is also what is shown in Fig. 8.

In a first phase, the direction of the maneuver to be applied is inferred. Automatic guidance of the aircraft is carried out along a direction tending to cancel out the deviation Δ. The direction of the guidance tends to cancel out the deviation and the intensity of the guidance order may be a proportional control of the type: Imp = k. 6average where 6average is the average of the display to the right and to the left of the fixed point. 16 In other words, the deviation between both displays gives a resulting display, and automatic guidance is carried out in the direction opposite to the observed resulting display.

In a second phase, a new targeted point may also be estimated as this will be seen later on in the subsequent text of the present description.

As this is seen in Fig. 6, the calculated automatic guidance maneuver may in most cases have the goal of deviating the aircraft 1 from the obstacle line 6, and therefore imparting to the aircraft 1 a lateral momentum Imp tending to cancel out β.

Therefore one has : Imp = Mass * V * F(P) With F( ) being a function of β, which shows that β is advantageously used in calculating the momentum .to be imparted to the aircraft.

As this will be seen in the following present description, F( ) may be of the sin (β) or tan (β) form.

A proportional control of the type: Imp = k. 6average 17 may also be contemplated instead of a momentum for cancelling out β.

Generally, - for lateral guidance along the X axis, the guidance of the aircraft is servo-controlled on a zero display deviation, in order to avoid the obstacles, and - for vertical guidance along the Y axis, the guidance of the aircraft is servo-controlled on a nonzero deviation.

The non-zero deviation is advantageous mainly in two flying situations: - in flying at a constant height; and - in a ground-approach phase and in landing.

When the velocity vector V of the aircraft 1 is aligned or parallel to the longitudinal axis of the aircraft, and for displays along a horizontal axis, it may considered that, the observations of displays are made in the reference system of the aircraft.

The reference system of the aircraft may also be used in a certain case for observing displays, for example for compensating the incidence of the aircraft relatively to the horizontal during flying at constant 18 height or for optimizing the observation of the displays during approach of the ground or the landing.

Thus, when the non-zero threshold becomes too large, it is preferable to have the sensor pivot towards the ground in order to observe the continuous displays.

As this is shown in Fig. 10, when the velocity vector V of the aircraft is neither aligned nor parallel with the longitudinal axis of the aircraft 1, typical of a ground-approach phase or a landing - and generally for displays along a vertical axis, the display observations are made in the aerodynamic reference system of the aircraft, i.e. the reference system no longer aligned on the longitudinal axis of the aircraft but on the velocity vector V.

The sensor 3 is therefore mounted with possible pivoting relatively to the aircraft so as to be constantly aligned with the velocity vector V of the aircraft .

As this has been stated in a general way, a normal mode for automatic guidance of the aircraft, along at least one tolerance direction, may involve servo- control of the guidance of the aircraft around a deviation between quantities related to the display. The deviation should be less than or equal to a predetermined threshold, the threshold being non-zero. 19 The aforementioned non-zero threshold assumes all its sense in the vertical direction Y.

As this is shown in Fig. 9, upper and lower displays relatively to the fixed point 5 are dissymmetrical. Indeed, the upper displays correspond to the sky (very little patterns moving past in general) and the lower displays correspond to the display of the ground (many patterns continuously passing by and displayed) . The predetermined threshold takes into account the display dissymmetry and gravity. For this purpose, one sets: Threshold = fixed display acceptable for a set flight height Hvol, whence Threshold = Hv°l Dis tan ce _ D The distance D is a fixed value guaranteeing the maneuvering time, for example for twenty seconds of flight, one has Distance = V (aircraft) *20 i.e. for a velocity of 100 m/s, a distance of 2,000 m. The servo-control on this set value causes the guidance system to maintain the aircraft at Hvol with an advance of 2,000 m (or 20 seconds) . 20 The maneuver for avoiding the obstacle will only be carried out when the deviation between the displays will be above the threshold, i.e. when the aircraft excessively approaches the ground for example. Thus, automatic guidance of the aircraft, along the tolerance direction and tending to find a deviation less than or equal to the predetermined threshold, is triggered when the deviation is above said threshold.

Of course, if it is desired that the aircraft remains in proximity to an obstacle placed sideways relatively to the aircraft, a non-zero predetermined threshold for the deviation will be applied to the horizontal direction X.

A specific automatic guidance mode of the aircraft along said direction of tolerance may be triggered in order to maintain a deviation equal to a predetermined approach threshold. For example, this is then a ground approach and/or a landing phase.

In the aforementioned specific mode, the deviation is then determined and the guidance of the aircraft is corrected in order to make it equal to the predetermined approach threshold. Such a specific guidance mode allows the aircraft to properly approach the ground.

It is recalled that during an approach phase, the sensor may be pivoted towards the ground in order to be aligned with the velocity vector of the aircraft. 21 The guiding orders are to be applied in the aerodynamic reference system of the aircraft. It is therefore supposed that the estimation of the incidence and side-slip is under control. The estimation may be negligible in certain cases, or in any case compensated at the flight control system.

Very preferentially, the width of the field 4 is a function of the quantities.

Indeed, the efficiency of the method is improved if the quantities are determined as earlier as possible, i.e. in a field 4 as narrow as possible, while making sure that these quantities are significant.

Now, the dynamics may strongly vary depending on the type of relief and topography encountered by the aircraft.

The processing of the field should only retain the information related to the quantities related to the display due to the progression of the aircraft 1 in the environment .

The aforementioned piece of information may typically be obtained by the following successive processing operations: - stabilization of the image: the "high frequency" attitude movements of the aircraft are filtered out in 22 order to obtain a stable resulting image on the targeted point of the aircraft, the quantities related to the display due to progression of the relief are obtained by means of a strong assumption which is recalled: the objects to be observed are fixed and the velocity of the aircraft is known. The prediction of the expected display may be made accurately if the order of magnitude of the distance is known. It is therefore sufficient to continuously estimate the distance with a suitable algorithm.

The following developments relate to the optimization of the method described above. Optimization is carried out by adapting the field of- the sensor, in order to compensate for the observation discrepancies when the relief varies. Optimization is similar to controlling the focal distance of the sensor in order to retain at best a measurable order of magnitude in the field of the sensor.

The width of the field is calculated along two axes: horizontal and vertical axes. The width along the vertical axis and the width along the horizontal axis may be adapted in size independently of each other.

The following standard method may be applied: - the size of the field is reduced to its minimum size; 23 - the quantities are determined; - if the quantities in the field are too small, provision is made for increasing the calculation window, until the dynamics of the measurements reach a predefined threshold; - conversely, if the dynamics of the quantities become too strong (too large values on the edges of the field}, the size of the field should decrease.

Once the width of the field is adjusted to the proper dynamics, it may be considered that the average distance of the obstacle has been obtained. It is possible to apply standard techniques for continuous estimation, such as for example prediction of the distance and of the width of the field. Thus, one permanently has a standardized field width, i.e. optimized for determining the quantities.

Adaptation of the width of the field is carried out for example by means of an optical zoom in the sensor 3.

The angular precision of each pixel may also be adjusted depending on the measured quantities.

In parallel with adaptation of the width of the field, preferably along the horizontal axis and along the vertical axis, the deviations preferably also along the 24 horizontal axis and along the vertical axis, are used by the guiding function.

With this step, it is possible to increase the robustness of the guidance, even when the topography of the medium suddenly changes or even when one passes from an environment of the gentle or low relief type to an urban environment .

According to an alternative of an aircraft according to the invention, the aircraft 1 includes two sensors 31 and 32.

Thus, a quantity related to the differential display between both sensors 31 and 32 is detected on the same points. This alternative is especially advantageous in the case of lateral guidance.

The steps consisting of determining at least two quantities related to the continuous display of the environment and of determining the deviation, are carried out in the field of each sensor.

Guidance is then carried out depending on the differential of the deviations of the sensors 31 and 32.

As shown in Fig. 11, both sensors 31 and 32 are mounted in the plane perpendicular to the longitudinal axis 50 of the aircraft, at a distance Dstereo from each other . 25 Utilization of the difference of the display deviations observed by the two sensors provides further accuracy in estimating the characteristics of the obstacles. The significance may be strong, notably in an urban environment.

According to another alternative, in the case of minidrones or microdrones, moving in an urban environment, or even indoors, the display monitoring area completely surrounds the targeted point .

The estimation model and the associated image processing operations for determining the quantities related to the display have strong differences with flying over the relief continuously. Notably, the dynamics of the display are much more significant, with possible discontinuities.

On the other hand, it may be expected that the monitored contours are clearer, whence a better ratio of the signal-to-noise (SNR) intensity for these quantities, with piecewise continuity.

Advantageously, the masked areas are taken into account. For this purpose, it is of interest to store in memory the obstacles perceived very early, having momentarily disappeared and the reappearance of which may be predicted on the path of the aircraft. 26 In the foregoing developments, the quantity related to the continuous display is the display of a pattern, or an average value of a plurality of displays.

According to an alternative or additionally, the quantity related to the display is the time derivative of the display. The time derivative is rich in information. With it, the trajectories of the obstacles may be tracked as early as possible. In other words, if the image processing step gives rather rich results, this may be a way of anticipating the closing-in of obstacles. It is recalled that as regards two-dimensional tracking, the time derivative of the display, associated with an initial three-dimensional condition - even inaccurate -on the position or the velocity allows the trajectory of objects to be estimated and completely predicted in 3D.

The following developments describe a possible embodiment of the means for applying a method according to the invention.

As this is shown in Fig. 7, the means 100 of the aircraft 1 allow application of the guidance function.

The guidance function is the target function to be adjusted relatively to the overall behavior of the aircraf 1 and of the sensor 3. The overall behavior notably includes the flight control and the dynamics of the aircraft 1. 27 From an image stemming from the sensor 3 and until elaboration of the guidance maneuvers to be applied to the aircraft 1, the guidance function is for example achieved in four successive steps: - determination of the horizontal display; - determination of the arrival angle on the obstacle and of the remaining time before collision; - calculation of the horizontal momentum required for avoiding the obstacle; - calculation of the acceleration term to be applied to the aircraft, and for which duration.

The module 101 carries out the determination of the quantities. For this purpose, it is capable of carrying out image processing in order to for example determine the display on the left and on the right of the fixed point 5 of the field. As an input parameter, it has the image perceived by the sensor 3 onboard the aircraft 1 and as output parameters for example the display on the left of the fixed point 5 and the display on the right of the fixed point 5.

During the determination of the quantities, the displacements of objects due to the closing-in onto the aircraft have to be isolated. The determination may be carried out on the stabilized image, and in particular on 28 the image in which high frequency displacements, characteristics of vibrations and erratic attitude variations of the aircraft have be filtered out.

It is specified that in the case of flying over low altitude relief, the display model is strongly predictive .

The model 102 is capable of estimating the obstacle, through purely geometrical considerations such as the angular misalignment of the area observed in the image: a. It has as input parameters - 5g - the display on the left of the fixed point - , - 8d - the display on the right of the fixed point -and - the velocity V of the aircraft.

It has as output parameter - Tc - the time before collision and - β - the estimated angle of the obstacle line.

In a first phase, the displacements measured on the right and on the left allow an estimation of the distances Dd and Dg : 29 Dd V.sin a/5d, Dg V.sin a/5g.

As shown in Fig. 6, the guidance order is calculated so that the aircraft 1 flies along the obstacle. Geometrically, this is expressed by the fact that the obstacle appears to the aircraft with an angle β as small as possible.

The narrowing of the field allows the following approximations to be made: tan β = Bd/hl = Bg/h2 One also has Bd = Dd * sin a; and HI = Hd * cos a Similarly Bg = Dg * sin a 30 H2 = Hg * cos a Therefore 2 * Dd tan ? = * ian a Dd - Dg\ Which may also be written Which may also be written depending on the measured displays 5g and 5d: It is understood that the sin β value may easily be inferred from the value of tan β.

The module 103 is capable of carrying out the calculation of the avoidance maneuver. There again, the operation of module 103 is based on geometrical considerations. It is independent of the dynamic characteristics of the aircraft . It has as input parameters 31 - β, - V, - the inertia of the aircraft, - the direction of the continuous display {i.e. the sign of 5g - 5d) .

It has as an output parameter Imp - the momentum to be applied.

In most cases, the momentum is adjusted for canceling out β. The goal is that upon completion of the maneuver, the aimed point is at infinity until a new obstacle line is encountered.

A typical guidance strategy may be the following.

When the difference of the right and left continuous displays |5g - 5d| is significant, i.e. that it is not marred by uncertainties, the order is applied: Imp = Mass * V (aircraft) * F(P) Advantageously (β) is sin β.

So one has 32 Imp = Mass * V (aircraft) * Ξίη(β) This equation shows that the value of β is taken into account in calculating the momentum to be given to the aircraft. The calculation of tan β shows that the guidance order takes directly into account the measured displays (see equation (E) above) .

In certain cases, F (β) may be of the tan β form.

When the difference of right and left displays |5g -5d| may be marred by uncertainties, for example in the case when the observed difference |5g - 5d| is too small, nothing can be decided.

The average value of the displays in the image is then monitored: |5g - 5d| / 2.

It should be noted that the estimation of the remaining time before collision, i.e. : Tc = (Dg + Dd) / (2V) is directly related to this average value. Tc indeed has approximately the value: Tc o verage * 0t 33 If Tc is small, then the risk is distant, and the guidance order may be zero.

If Tc is significant, the case is very particular, when the obstacle is dangerously close and appears perpendicularly. In this case, an emergency strategy applying an order in an arbitrarily selected direction is the solution.

Of course, a proportional control of the type Imp = K. δaverage where 6average is the average of the displays on the right and on the left of the fixed point, may also be contemplated .

The direction of the maneuver is given by the sign of 6g - 6d.

The module 104 is capable of calculating the horizontal acceleration term. It is at the boundary of the guidance function and of the flight control module which is strongly related to the characteristics of the aircraft (types of flight control surfaces, inertia, mass, flight domain,...)/ It has as an input parameter Imp.

It has as an output parameter 34 - Acc - the order of horizontal acceleration - and - Dt - the duration of application of the order.

The order depends on the transfer function of the flight control loop of the aircraft. any case the following is observed Imp = Acc * D . 35

Claims (20)

1. A method for guiding an aircraft (1) in an environment (2), the aircraft (1) including at least one sensor (3) having an optical field (4) for observing the environment, the environment (2) being continuously displayed in the field (4) of the sensor (3), during the movement of the aircraft, relatively to a fixed point (5) at the centre of the field (4) , characterized in that it includes a step consisting of: . . -, . · , f c dd> dS7 determining at least two quantities (

2. The method according to claim 1, including a step consisting of determining two quantities related to the horizontal continuous display of the environment on a horizontal axis (X) in the field (4) and/or two quantities related to the vertical continuous display of the environment on a vertical axis (Y) in the field (4), the direction of the automatic guidance along a direction parallel to the horizontal axis (X) and/or along a direction parallel to the vertical axis (Y) depending on the deviation between both quantities on each axis (X, Y) .

3. The method according to claim 2, wherein the automatic guidance of the aircraft along at least one direction is carried out along a direction tending to cancel out the deviation.

4. The method according to any of claims 2 or 3 , wherein a normal automatic guiding mode of the aircraft, along at least one direction of tolerance, involves servo-control around a deviation less than or equal to a predetermined non-zero threshold, and automatic guidance of the aircraft along said direction of tolerance tending to again find a deviation less than or equal to said predetermined threshold being triggered when the deviation is above said threshold.

5. The method according to claim 4, wherein the direction along which the deviation is involved is the vertical direction. 37

6. The method according to any of claims 4 or 5, wherein a specific automatic guidance mode of the aircraft along said direction of tolerance is triggered in order to maintain a deviation equal to said predetermined threshold.

7. The method according to any of claims 1 to 6 , wherein the width of the field {4) is adjusted according to the quantities.

8. The method according to any of claims 1 to 7, wherein the angular precision of each pixel is adjusted according to the quantities.

9. The method according to any of claims 1 to 8, wherein the aircraft (1) includes two sensors {31, 32), the steps consisting of determining at least two , „ dd, άδΊ . , , quantities (

10. The method according to any of claims 1 to 9 , wherein the guidance intensity depends on the absolute value or the average of the quantities.

11. The method according to any of claims 1 to 9, wherein, when the deviation of the quantities is 38 significant, the intensity Imp of the guidance is of the form Imp = Mass * V (aircraft) * Ρ(β) wherein mass is the mass of the aircraft, V (aircraft) is the velocity of the aircraft, and wherein Ρ(β) is a function of β, where β is the angle between a line of obstacles to be avoided and the direction of movement of the aircraft.

12. The method according to any of claims 1 to 11, wherein the quantity related to the continuous display is the actual display or an average value of a plurality of displays .

13. The method according to any of claims 1 to 12, wherein the quantity related to the display is the time derivative of the display.

14. An aircraft (1) capable of moving in an environment (2) , including at least one sensor (3) having an optical field (4) for observing the environment, the environment (2) being continuously displayed in the field (4) of the sensor (3), during the movement of the aircraft, relatively to a fixed point (5) at the centre of the field (4) , 39 characterized in that it includes means (100} for: - determining at least two quantities related to the continuous display of the environment, a quantity being located on one side of the fixed point (5) and another quantity being located on another side of the fixed point (5) ; - determining a deviation (Δ) between both quantities; - automatically guiding the aircraft in the environment, a guidance direction being a function of said deviation.

15. The aircraft according to claim 14, wherein the sensor is rotationally mobile about an axis.

16. The aircraft according to any of claims 14 or 15, including two sensors. 40

17. The method according to any one of claims 1-13 substantially as described in the specification and in the foregoing claims.

18. The method according to any one of claims 1 -13 substantially as illustrated in any of the drawings.

19. The aircraft according to any one of claims 14-16 substantially as described in the specification and in the foregoing claims.

20. The aircraft according to any one of claims 14-16 substantially as illustrated in any of the drawings. P-11160-1 L