FR2745785A1 - METHOD AND DEVICE FOR GUIDING A FLYING BODY TO A TARGET - Google Patents

Abstract

The present invention relates to a method and a device for guiding a flying body (M), in particular a missile, towards a target (C), said flying body (M) comprising an image sensor. According to the invention, when approaching the target (C): - in a first phase, when the target (C) is detected in an image of the image sensor:. the angle (THETAo) between the line of sight (LV) of the image sensor and the longitudinal axis (AL) of the flying body (M) is kept constant; and. a trajectory (T1) is imposed on the flying body (M) such that the target (C) is kept fixed in the image; then -in a second phase, the flying body (M) is guided directly (T2) towards the target (C).

Description

The present invention relates to a method for guiding a flying body

  towards a target, located on the territory overflown by the said flying body, as well as a device for

the implementation of this method.

  Although not exclusively, the present invention applies more particularly to a missile, for example a missile

  anti-tank, comprising an image sensor which observes, towards the bottom and towards the front of the missile, following a line of sight, said territory overflown. In the context of the present invention, the image sensor relates to a sensor which renders, in the form of an image, a vision of reality.

  Generally, the line of sight of said image sensor is kept fixed, in position to be stitched, with respect to the missile, during the search phase of the target, and at least until detection of the latter. In known manner, such a target search mode is implemented,

  particularly on missiles equipped with infrared or visible image sensors.

  After the detection of the target, the missile is generally aligned with said target, and then guided directly on the target, often by autoguiding. Such an alignment

  of the missile on the target causes the exit of the target from the field of view of the image sensor, if the line of sight of the latter is maintained in its initial position, to pitch, with respect to the longitudinal axis of the missile so that, in this case, the missile can no longer receive informa-

  said image sensor relating to the target, which makes it impossible to precisely guide said missile, in particular by autoguiding.

  Two known solutions can be envisaged to obtain then, despite everything, information concerning the target: - first, use a mobile image sensor, mounted on a stabilized platform. This solution implemented on many missiles is technically satisfactory, but it is expensive and complex. The presence of a double platform, in fact, virtually the cost of the front part of the missile, in particular because

  mechanical and electrical complexity, servitude

  additional motorizations and engines, and the difficulty of assemblies and integrations; and second, use an image sensor having a very wide field of view to encompass the axis of the missile. This solution, however, results in a degradation of the angular resolution of the image sensor, which reduces the detection and recognition distances of the target. In addition, all the upper part of the image

  formed then is useless, since it visualizes the sky.

  Therefore, neither of these two known solutions has both high efficiency and low cost, and can not be considered satisfactory, especially

for cost-reduced missiles.

  The present invention aims to remedy these problems.

  disadvantages. It relates to a method for guiding, precisely and inexpensively, a flying body, particularly a missile, towards a target located in the territory overflown by

  the flying body, said flying body comprising an image sensor which observes, downward and forward of the flying body, along a line of sight, said territory over-30.

  For this purpose, according to the invention, said process is remarkable.

  in that, when approaching the target: in a first phase, which starts when the target is detected in an image generated by the image sensor: the angle between said line of aiming the image sensor and the longitudinal axis of said flying body; and A imposes on said flying body a trajectory such that the target is kept fixed in the image; then - in a second phase, which starts when the maximum load factor that can be applied to the said flying body corresponds to the load factor that must be

  applied to said flying body to curve said trajectories

  in order to reach said target, said flying body is guided directly towards said target, by applying said

maximum load factor.

  Thus, thanks to the invention, as during said first phase: the angle between the line of sight and the longitudinal axis of the flying body is kept constant, it is possible to use a fixed line-of-sight image sensor. the flying body, that is to say a low cost image sensor, not requiring a stabilized platform for its implementation; and since the target is maintained in the image, information is received throughout said first phase concerning said target, and in particular the position thereof, which makes it possible to carry out extremely precise guidance of the body

  flying, especially in the form of autoguiding.

  The present invention therefore satisfies both conditions

  mentioned above of efficiency and reduced cost. It also has other advantages when it is implemented,

  - easy assembly and maintenance;

  - a saving in components, especially in electronic components

  picnics; and - in the case of a missile, a significant simplification

  automatic tests to be done before firing.

  Advantageously, in said first phase, to guide said flying body along said imposed trajectory: a first control command is calculated to guide said flying body in a vertical reference plane passing through said flying body and said target ; and a second control command, for guiding said flying body in the horizontal plane; and - applying to said flying body said first and second

order orders calculated in this way.

  The process according to the invention can be implemented

  according to two different modes of implementation specified below.

  In a first mode of implementation, said first order

  command is a command order of the load factor of the flying body, applying a command load factor.

  In this case, advantageously, the control load factor rco is calculated from the following expressions: rco = (V2. (D2z / dx2)) / (l + (dz / dx) 2) 3/2 - (zK (xc-x)) dz / dx = (Kz) + (xc-x) - (dz / dx). (xcx + K2. (xc-x)) - z (K2 + 1) d2z / dx2 = (K.z + (xc-x)) 2 in which: - K is a gain value; x is the distance between the flying body and a reference point, in a horizontal direction of said vertical reference plane; z is the distance between the flying body and said reference point, in a vertical direction of said vertical reference plane; xc is the distance between the target and said reference point, in said horizontal direction, of constant value; and - V is the value of the projection of the velocity vector of the

  body flying on said vertical reference plane.

  The calculation of said control load factor can be

  realized according to different embodiments.

  In a first embodiment, for calculating said control load factor rco, the following is used: for the gain K, a predefined constant value; and - for the distances x and z of the flying body, values

  determined from accelerometric measurements carried out

on said flying body.

  Furthermore, in a second embodiment, for calculating said control load factor Fco: - the gain K is calculated from the equation K = tg (a-Oex), in which: 25. a represents the position angular of the target in the image taken by the image sensor; and eex is the value of the longitudinal attitude performed by the flying body; and the distances x and z of the flying body are determined from accelerometric measurements made on said flying body. In this case, preferably, the angle α is determined from measurements taken by an image follower, on an image

taken by said image sensor.

  In order to overcome the imperfections of execution of the control load factor specified above, due in particular to the existence of delays, response time, bias and / or noise in the execution and likely to cause a displacement of the target in the image, we add a term

  additional correction to said control charge factor.

For this purpose, according to the invention:

  - a corrective acceleration calculated

  to generate an action opposing the displacement of the target in the image; and - the corrective acceleration thus calculated is added to

  control load factor to be applied to the flying body.

  Preferably, said corrective acceleration r1 is cal-

  based on the expression: ## EQU1 ## in which: a is a constant, preferably equal to 3; - at is the speed of angular displacement of the target in the image; and - Vr is the speed of approach of the target's flying body (which is close to the speed of said flying body

  when the target is weakly mobile).

  Moreover, in the second mode of implementation of

  the invention, said first control command is a control command of the longitudinal attitude of the flying body, applying a longitudinal control attitude.

  In this case, in particular to remedy the imperfections of execution of said longitudinal control plate, one calculates and applies to said flying body, in addition to said

  longitudinal control pitch, correct acceleration

  which creates an action against a possible

  moving the target in the image.

  In addition, when said flying body is guided by means of control surfaces, and said longitudinal control attitude and said corrective acceleration are calculated and each applied by means of a specific control loop, advantageously, it is operated in parallel. said control loops so as to obtain two separate steering commands of the control surfaces of the flying body which are applied

  simultaneously to the control surfaces of said flying body.

  Advantageously, in order to calculate the corrective acceleration, account is taken of the angular velocity and the acceleration of the flying body that can be generated by the application of the longitudinal control attitude, which must be

  applied simultaneously to said corrective acceleration.

  Preferably, said water angular velocity and said False acceleration are calculated from the following expressions: false = external = V. Oco in which:

  - Oco is the angular velocity obtained from the

  longitudinal control; and - V is the value of the projection of the velocity vector of the

  body flying on said vertical reference plane.

  Furthermore, advantageously: in a first embodiment, said second phase is started when the derivative e with respect to the time of the actual deviation value (rotation of the line engincible in the ground reference) becomes equal to a maximum value emax which verifies the equation: kmax = (rmax-A) / (BV) in which: 5. A and B are two predefined constants; At rmax is said maximum load factor; and V is the value of the projection of the velocity vector of the flying body on said vertical reference plane; whereas - in a second embodiment, said second phase is started when the longitudinal control plate

  becomes equal to a limit value of longitudinal

  nal, obtained by the application to the said flying body

  maximum load factor, taking into account the

  aunt of turning time of the flying body.

  The present invention also relates to a device for implementing the aforementioned method, said device being mounted on board a flying body and comprising: - an image sensor for taking along a line of sight images of the territory overflown;

  - a system of calculation to determine orders of com-

  said flying body, from images taken by said image sensor; and control means for applying to said flying body the control commands determined by said calculation system.

  For this purpose, according to the invention, said device is remarkable

  in that: - the line of sight of the image sensor is fixed with respect to the longitudinal axis of the flying body; and said calculation system determines control commands enabling: in said first phase, to impose on said flying body a trajectory such that the target is held fixed in the image; and in said second phase, guiding said flying body directly towards said target. The figures of the annexed drawing will make clear how

  the invention can be realized. In these figures, references

  Identical references designate similar elements.

  Figure 1 schematically illustrates the guidance according to

  the invention of a body flying towards a target.

  Figure 2 shows the projection on a vertical plane of the

representation of Figure 1.

  FIG. 3 is a block diagram of a device according to

me to the invention.

  FIG. 4 schematically illustrates a first embodiment of calculation means, for the implementation of

  the invention according to a first embodiment.

  Figure 5 schematically illustrates a second mode of

  embodiment of calculating means, for the implementation of the invention according to said first mode of implementation.

  Figure 6 schematically illustrates a third mode of

  realization of calculation means, for the implementation of the invention according to said first mode of implementation.

  FIG. 7 schematically illustrates calculation means,

  for the implementation of the invention according to a second mode of implementation.

  The device 1 according to the invention is mounted on a flying body M, for example a missile, for guiding said flying body M towards a target C, for example a tank.

  destroy, illustrated by a point in Figures 1 and 2.

  Said device 1 diagrammatically represented in FIG. 3 is of the type comprising: an image sensor 2, for example with infrared or visible radiation, for taking on a field of

  vision CV formed around a LV line of sight representing

  FIG. 1 shows images (not shown) of the territory S overflown by said flying body M, in which territory S is located said target C; a calculation system 3 for determining control commands of said flying body M, from images taken by said image sensor 2; and control means 4, of the known type, for applying to said flying body M the control commands determined by said calculation system 3, so as to guide the flying body M, as illustrated by a mixed line G. According to FIG. According to the invention, the guidance of the flying body M by means of said device 1 has the following characteristics when approaching the target: in a first phase, which starts when the target C is detected in an image generated by the image sensor 2: the angle Oo is maintained constant between said line of sight LV of the image sensor 2 and the longitudinal axis AL of said flying body M; and imposing on said flying body M a trajectory T such that the target C is kept fixed in the image; then - in a second phase, which starts when the maximum load factor likely to be applied to said flying body M corresponds to the load factor which must be applied to said flying body M to curve said trajectory T in order to reach said target C, guide said flying body M directly to said target C,

  applying said maximum load factor.

  To do this, the device 1 is such that: the line of sight LV of the image sensor 2 is kept fixed with respect to the longitudinal axis AL of the flying body M; and said calculation system 3 determines control commands enabling: in said first phase, to impose on said flying body M a portion T1 of the trajectory T such that the target is held fixed in the image; and in said second phase, to guide said flying body M directly to the target C, as illustrated by the

  part T2 of the trajectory T of FIG.

  Thus, thanks to the invention: - as the line of sight LV is kept fixed relative to

  the longitudinal axis AL of the flying body M, it is possible to use

  ser a low-cost image sensor 2 directly mounted, fixed station, on the flying body M and requiring no platform stabilized for its operation, which reduces the cost of the device 1; and the target C being maintained in the image, during all of said first phase, information is received throughout said phase concerning said target C, which allows

  to achieve extremely precise guidance.

  In addition, said device 1 has, in addition to a reduced cost and a precise implementation indicated above, other important advantages, in particular: - a simplified assembly and maintenance; - a saving in components, especially in electronic components; and - in the case of a missile, a significant simplification

  automatic tests done before the shot.

  More precisely, in order to be able to guide, in said first phase, said flying body M along said imposed trajectory T1, said computing system 3: calculates at the same time: a first command order specified below, to guide said flying body M in a vertical reference plane OXZ passing through said flying body M and said target C; and at a second command order, for guiding said flying body M in a horizontal plane OXY, said OXZ and OXY planes forming a reference reference OXYZ defined for

  explain the implementation of the present invention.

  According to the invention, in said horizontal plane OXY, the flying body M is guided according to a usual method which is not further specified, preferably a method of the "proportional navigation" type; and - transmits said first and second command orders

  to said control means 4 via a link 5.

  For this purpose, according to the invention: in a first embodiment of the invention, said first control command is a control command of the load factor of the flying body M, applying a command load factor Fco . Said calculation system 3 comprises for this purpose calculation means 6, 7 or 8 shown in three different embodiments respectively in Figures 4 to 6, for calculating said control load factor rco; while - in a second embodiment of the invention, said first control command is a control command of the longitudinal attitude of the flying body, applying a longitudinal control attitude eco, calculated by computing means 9 , integrated in the said system of

  calculation 3 and diagrammatically shown in FIG. 7.

  According to the invention, in said first mode of implementation of the invention, the control load factor rco calculated by one of said calculation means 6, 7 or 8, is obtained in particular from the following expressions, explained hereinafter: rco = (V2. (d2z / dx2)) / (l + (dz / dx) 2) 3/2 (1) - (zK. (xc-x)) dz / dx = (2) (Kz ) + (xc-x) with - (dz / dx). (xc-x + K2. (xc-x)) - z. (K2 + 1) d2z / dx2 = (3) (K.z + (xc- x)) 2 in which: - K is a gain value specified below; x is the distance between the flying body M and a point of

  reference, in this case the point O of the reference

  OXYZ cited above, in the horizontal direction OX, as shown in Figures 1 and 2; z is the distance between the flying body M and said reference point O, in the vertical direction OZ of said vertical reference plane OXZ; xc is the distance between the target C and said reference point O, in said horizontal direction OX, of supposed constant value; and - V is the value of the projection of the velocity vector of the

  flying body M on said vertical reference plane OXZ.

  Note: - that dz / dx and d2z / dx2 correspond to the first derivatives

  and second of a function z = f (x) which represents the projection

  on the plane OXZ of the portion T1 of the trajectory T of the flying body M in said first phase, said trajectory portion T1 being imposed to maintain the target C fixed in the image with a constant angle GB between the line of sight LV and the longitudinal axis AL of the flying body M. As can be seen in FIG. 1, according to the invention, the line of sight LV is not necessarily aligned with the target C, that is, say that the target C is not necessarily in the center of the image. It is sufficient for the implementation of the invention that the

  target C is located in said field of view CV. generation

  Meanwhile, the target C is maintained in the image, throughout the trajectory portion T1, at the position it occupies at the beginning of said first phase. However, another position may also be considered. For some

  reasons for simplifying the presentation of the invention

  In FIG. 2, line of sight LV has been aligned on target C; and

  - that the command load factor rco verifies the equa-

  rco = V2 / R, with R the radius of curvature of the curve

  z = f (x), that is R = (1 + (dz / dx) 2) 3/2 / (d2z / dx2).

  Now, with reference to FIG. 2, the calculation of the above-mentioned expression (2) relating to

  the trajectory portion T1 imposed in the vertical reference plane OXZ.

  We consider for this purpose a corresponding function zl = f (xl)

  to the function of the trajectory part T1 sought in said plane OXZ to maintain a constant angle eo.

  It is assumed, first of all, that the velocity vector V of the flying body M is located on the longitudinal axis AL of the missile, that is to say that the angle B between said vector V and said longitudinal axis AL is null (this simplifies the calculations, but the case B # 0 does not call into question the validity

of the process used).

  By definition, the angle Oo verifies the following expression: Go = Ocible Omis, - Omis being the longitudinal attitude of the flying body M defined from the horizontal H passing through the flying body M; and - Ocible being the longitudinal attitude which the flying body M must have to point directly to the target C. By putting K = tgOo, tgOo representing the tangent of the angle Go, we obtain from tgOcible - tgemis K = l + ( tgOcible tgOmis) that is tgOcible - K tgOmis = l + (K.tgecible) Moreover, according to the definition of the function zl = f (xl) and as B13 is assumed to be null, the following expressions are 15 also checked: tgOmis = -dzl / dxl tgOcible = zl / (xc-x) = f (xl) / (xc-x) Using the preceding expressions, we easily deduce the nonlinear differential equation: - (f (xl) - K. (xc-x)) dzl / dx1 = (4) (Kf (x1)) + (xc-x) From the initial conditions of this equation (4) and

  taking into account the incidence introduced by a non-zero angle B, the expression (1) above is finally obtained.

  The use of this expression is now described (1)

  in the implementation of the invention.

  As indicated above, the calculation means 6, 7 and 8 respectively represented in FIGS. 4 to 6 calculate, according to three different embodiments, the

  control load rco, using said expression (1).

  In the first embodiment of FIG. 4, the calculation means 6 use, in the calculation of the control load factor rco: for the gain K, a predefined constant value; and - for the distances x and z of the flying body M, values

  determined from accelerometric measurements carried out

  These calculating means 6 comprise for this purpose: - an integration element 11 which receives, by a link 12 of a suitable device 13, for example an inertial unit, the value Fzex of the acceleration performed by the flying body M in said direction OZ, and which determines, from a double integration of said value rzex, said distance z; an integration element 14 which receives, by a link 15, also said device 13 or another appropriate device not shown, for example a specific accelerometer, the rxex value of the acceleration performed by the flying body M according to said direction OX, and which determines, from a double integration of said rxex value, said distance x; and - a calculation element 16 comprising in memory the predefined constant value of the gain K, connected via links 17 and 18 respectively to said integration elements 11 and 14, calculating the control load factor rco from l expression (1) above and

  likely to transmit the result obtained by

  link 19, which can be linked to the

link 5 of FIG.

  It will be noted that the figures have been shown, whenever necessary, in parentheses in the

  following link references, the information transmitted

  its by these connections, as for example the control load factor rco transmitted by the link 19 of FIG. 4. In the second embodiment shown in FIG. 5, the calculation means 7 also comprise said elements 11, 14 and 16, but they additionally comprise elements 20, 21 and 22 to determine in real time the

  gain K and integrate it into the calculation of the command load factor rco.

  For this purpose, said element 20 is an integrating element which integrates the speed of displacement of the target C onto an image taken by the image sensor 2 so as to obtain a value a representative of the displacement of the target C over the image. In known manner, said speed is

  directly extracted from the image by an image follower 23 which is connected to the image sensor 2 via a link 24 and which transmits said value to user devices, such as the integration element 20, via a link 25.

  The element 21 is also an integrating element for integrating the angular velocity Eex executed by the flying body M, received by a link 27 of a suitable gyrometric measuring means, which is for example integrated in the device 13, of in order to obtain the Eex value of the longitudinal plate executed by the flying body M. The values a and Oex thus calculated are transmitted,

  respectively via links 28 and 29, to the computing element 22 which then calculates in real time the gain K from the expression K = tg (a-Oex).

  Said calculation element 22 also transmits, in real time, the value K thus determined, by a link 30, to the calculation element 16 which then calculates the control load factor rco, as indicated above, from the Expression (1) above. In the third embodiment shown in FIG. 6, the control means 4 are transmitted as the first control command in addition to the load factor of

  rco command as calculated in the first embodiment.

  aforesaid, a corrective acceleration rl intended to generate an action opposing a possible displacement of

the target C in the image.

  This corrective acceleration Fri only provides an additional order whose only objective is to compensate for the imperfections in the execution of the control load factor rco, notably because of the existence of delays, of time

  response, bias and / or noise. Indeed, if the Fco control command was perfectly executed, the addition of this corrective acceleration ri would be useless, since the target C20 would then be held fixed in the image.

  For this purpose, the calculating means 8 comprise a calculation element 33 which calculates the corrective acceleration F1 from the expression: Fri = a. &. Vr25 in which: - a is a stored predefined constant, preferably equal to at 3; - & is the angular displacement speed of the target in the image, received from the image follower 23; and Vr is the approach speed of the flying body M of the target C. Said speed Vr can be transmitted to said

  computing element 33 by a known means not shown.

  Said calculation means 8 furthermore comprise a calculation element 34 which is the sum of the control load factor rco and the corrective acceleration Fri, received respectively via links 35 and 36, and which transmits the result by a link 37 that is, by

  example, connected to the link 5 of FIG.

  As indicated above, in the second embodiment of the invention, in said first phase, the first control command for the guidance in the first phase is applied.

  the plane OXZ, a longitudinal control attitude co calculated by the calculation means 9 represented schematically.

  Figure 7, and specified below.

  For reasons of precision of the guidance, it is necessary to generate moreover an action intended to compensate for any displacement of the target C in the image, due in particular to the imperfections of the execution of the command order

of the longitudinal attitude.

  For this purpose, we order more, in said first

  phase, a corrective acceleration F2 generating an action20 to oppose such a displacement of the target C in the image.

  According to the invention, said longitudinal control plate

  Oco and said corrective acceleration F2 are calculated from specific control loops, of which only the loop portions BC1 and BC2 which are integrated in said calculating means 9 have been represented respectively.

  Each of said loop portions BC1 and BC2 computes a

  steering order of the unrepresented control surfaces of the flying body M, as specified below.

  These two orders are added by a calculation element 40

  who receives them via links respectively

  41 and 42 of said loop portions BC1 and BC2, and which is capable of transmitting the result obtained by a link 43 connected for example to the link 5 of FIG. 3 so as to be able to simultaneously apply these two steering commands to the control surfaces of FIG. Flying body M. According to the invention, for calculating the steering order tcol relative to the longitudinal control plate Oco, the loop portion BC1 comprises: a calculation element 44 connected to said image follower 23 and

  determining the longitudinal pitch of the eco control.

  Said calculation element 44 uses for this purpose, on the one hand, the value of the displacement a of the target in the image, calculated from the value received from said image follower 23, and the value of the angle eo to be kept constant according to the invention; a calculating element 46 calculating an eco control angular velocity corresponding, in this case, to the derivative of the difference between said longitudinal control plate eco received by a link 47 and the longitudinal attitude executed Oex by the flying body M, said value Oex being received by a link 48 of an integration element 49 which is connected to the device 13 and performs the integration of the angular velocity executed Sex; and a calculation element 50 which determines, in known manner, said first steering order rcol, from said control angular velocity Oco received by a link 51.

and the angular velocity Oex.

  Furthermore, the loop portion BC2 comprises: a calculation element 53 connected to the image follower 23 to calculate a corrective acceleration r2, starting from the

  same expression as that used to calculate the acceleration

  corrective ration rl of the embodiment of Figure 6, namely F2 = a. &. Vr. This corrective acceleration F2 is intended to generate an action opposing a possible displacement of the target in the image, F2 being proportional to this effect at the speed of displacement & determined by the image follower 23; and a calculating element 54 determining a steering order tco2 of the control surfaces of the flying body, in known manner, from said corrective acceleration F2 (received by a link 55), of the acceleration executed Fzex according to the

  direction OZ, and the angular velocity executed Oex.

  However, in order to prevent the actions of one of the said

  BC1 or BC2 loop parts cause by their effects a reaction of the other, it is necessary to perform compensation between these two loop parts BC1 and BC2.

  Specifically, for the loop portion BC2 to engender only a correction of the displacement of the target C in the image, and not a correction of the effects produced by the loop portion BC1, said computation element 54 It does not directly use the acceleration Fzex executed and the angular velocity Sex performed in its calculations, but it uses a compensated acceleration Fcomp and an offset compensated angular velocity received respectively via links 56 and 57 and computed from the expressions: Fcomp = Fzex - False ecomp = ex - Waters in which: - Waters is an auxiliary angular velocity corresponding, according to the invention, to the eco-angular velocity which is transmitted by the split link 51 to an element of

  calculation 60, said calculation element 60 calculating the difference

  Oex-aco (i.e., comp) and transmitting this difference to computing element 54 via link 57; and - False is an auxiliary acceleration calculated by a calculating element 61 from the expression: False = V.àco, V being the aforementioned speed of the flying body M in the plane

vertical reference OXZ.

  This speed V is transmitted to said computing element 61 by a known means not shown. In addition, the difference (Fzex-False) is calculated by a calculation element 62 connected by links 56 and 63 to

calculation elements 54 and 61.

  It will be noted that the compensations used are the False and Oaux values mentioned above, since it is not possible to directly access the gyrometric and accelerometric values.

  performed by the flying body, in response to a command of the loop part BC1.

  As indicated previously, according to the invention, the trajec-

  T comprises two parts T1 and T2 relating respectively to said first and second phases of the guidance. The second phase, so also the trajectory part

  T2, begins when the flying body M is located at a horizontal distance d from the reference point O along the axis OX, as shown in FIG.

  To determine this position of beginning of second phase,

  the invention provides two different embodiments.

  In a first embodiment, said second phase is started when the derivative k with respect to the time of the real deviation value, obtained for example from the speed θ determined on an image and the value Oex, becomes equal to maximum value emax which verifies the equation: emax = (rmax-A) / (BV) in which: - A is a predefined constant, for example equal to 5 m / s2, taking into account the response time of the flying body

M;

  B is a predefined constant, for example equal to the above-mentioned constant; rmax is said maximum load factor; and - V is the value of the projection of the velocity vector of the

  flying body M on said vertical reference plane OXZ.

  Furthermore, in a second embodiment, said second phase is started when the longitudinal control attitude eco becomes equal to a longitudinal attitude limit value, obtained by applying said steering body M to said load factor. maximum rmax, taking into account the turning time constant of the flying body M.

Claims (22)

  1. Method for guiding a flying body (M), in particular a missile, towards a target (C) located on the territory (S) overflown by the flying body (M), said flying body (M) comprising a sensor 'images (2) which observes, downward and forward of the flying body (M), along a line of sight (LV), said territory overflown (S), characterized in that, when approaching the target (C): in a first phase, which starts when the target (C) is detected in an image generated by the image sensor (2): the angle (eo) between said line is kept constant the viewfinder (LV) of the image sensor (2) and the longitudinal axis (AL) of said flying body (M); and imposing on said flying body (M) a trajectory such that the target (C) is held fixed in the image; then - in a second phase, which starts when the maximum load factor likely to be applied to said flying body (M) corresponds to the load factor which must be applied to said flying body (M) to curve said trajectory (T) in order to join said target (C), said flying body (M) is guided directly towards said target   (C), applying said maximum load factor.   2. Method according to claim 1, characterized in that, in said first phase, for guiding said flying body (M) along said imposed trajectory (T): - a first command order is calculated, to guide said body flywheel (M) in a vertical reference plane (OXZ) passing through said flying body (M) and said target (C); and a second control command, for guiding said flying body (M) in the horizontal plane (OXY); and - said flying body (M) is applied to said first and   second order orders thus calculated.   3. Method according to claim 2, characterized in that said first control command is a control order of the load factor of the flying body (M),   applying a command load factor (rco).   4. Method according to claim 3, characterized in that the control load factor rco is calculated from the following expressions: rco = (V2. (D2z / dx2)) / (l + (dz / dx) 2) 32 - (zK. (Xc-x)) dz / dx = (Kz) + (xc-x) (dz / dx). (Xc-x + K2. (Xc-x)) - z (K2 + 1) d2z / dx2 = (K.z + (xc-x)) 2 in which: K is a gain value; x is the distance between the flying body (M) and a reference point (O), in a horizontal direction (OX) of said vertical reference plane (OXZ); z is the distance between the flying body (M) and said reference point (0), in a vertical direction (OZ) of said vertical reference plane (OXZ); xc is the distance between the target (C) and said reference point (0), in said horizontal direction (OX), of constant value; and - V is the value of the projection of the speed vector of the flying body (M) on said vertical reference plane (OXZ).   5. Method according to claim 4, characterized in that, for calculating said control load factor Fco, the following is used: for the gain K, a predefined constant value; and - for the distances x and z of the flying body (M), values   determined from accelerometric measurements carried out on said flying body (M).   6. Method according to claim 4, characterized in that, to calculate said control load factor rco: - the gain K is calculated from the equation K = tg (a-Oex), in which: a represents the angular position of the target (C) in the image taken by the image sensor (2); and 15. ex is the value of the longitudinal attitude performed by the flying body (M); and determining the distances x and z of the flying body from accelerometric measurements made on said body flying (M).   7. Method according to claim 6, characterized in that the angle a is determined from   measurements made by an image follower (23) on an image taken by said image sensor (2).   8. Process according to any one of claims 3 to 7,   characterized in that, furthermore: - a corrective acceleration (rl) is computed capable of generating an action opposing the displacement of the target (C) in the image; and the corrective acceleration (rl) thus calculated is added to the control load factor (rco) to be applied to the body flying (M).   9. The method of claim 8, characterized in that said corrective acceleration r1 is calculated from the expression: ri = a. & .Vr in which: - a is a constant; - at is the angular displacement speed of the target (C) in the image; and - Vr is the speed of approach of the flying body (M) of the target (C).   10. The method as claimed in claim 2, characterized in that said first command command is a control command of the longitudinal attitude of the flying body, applying a longitudinal control attitude. (Oco).   11. The method as claimed in claim 10, characterized in that, in said first phase, in addition to said longitudinal control attitude (Oco), a corrective acceleration (r2) is calculated and applied to said flying body which generates an action s' opponent to a   possible displacement of the target (C) in the image.   12. The method of claim 11, said flying body (M) being guided using control surfaces, and said longitudinal control attitude (Oco) and said corrective acceleration (r2) being calculated and applied each by means of a loop. specific order (BC1, BC2),   characterized in that the said control loops (BC1, BC2) are operated in parallel so as to obtain two separate orders (rcc, tco2) for steering the control surfaces of the flying body (M) that are simultaneously applied to the control surfaces said flying body (M).   13. Method according to one of claims 11 or 12, characterized in that, to calculate the acceleration correcting   tive (r2), account is taken of the angular velocity and the acceleration of the flying body which can be engen-5 by the application of the longitudinal control plate (Oco), to be applied simultaneously to said corrective acceleration (r2).   14. A method according to claim 13, characterized in that said angular velocity Waters and said acceleration raux are calculated from the following expressions: Oaux = eco ral = V.Oco in which:   - eco is the angular velocity obtained from the   longitudinal control seat (Oco); and V is the value of the projection of the speed vector of the flying body (M) on said vertical reference plane (oxz).   15. Process according to any one of claims 1 to   14, characterized in that said second phase is started when the derivative E with respect to the time of the real deviation value becomes equal to a maximum value emax which satisfies the equation: emax = (rmax-A) / (BV ) in which: A and B are two predefined constants; rmax is said maximum load factor; and - V is the value of the projection of the speed vector of the flying body (M) on said vertical reference plane (OXZ).   16. Process according to any one of claims 1 to   14, characterized in that said second phase is started when the longitudinal control attitude (Oco) becomes equal to a longitudinal attitude limit value, obtained by applying to said flying body (M) said load factor maximum, taking into account the time constant   turning the flying body (M).   17. Device for implementing the specified method   according to any one of claims 1 to 16, said device (1) being mounted on board a flying body (M) and   comprising: - an image sensor (2) for taking along a line of sight (LV) images of the territory overflown (S); - a calculation system (3) for determining control commands of said flying body (M), from images taken by said image sensor (2); and control means (4) for applying to said flying body (M) the control commands determined by said computing system (3), characterized in that: - the line of sight (LV) of the image sensor ( 2) is fixed with respect to the longitudinal axis (AL) of the flying body (M); and said calculation system (3) determines control commands enabling: in said first phase, to impose on said flying body (M) a trajectory (T) such that the target (C) is held fixed in the image; and 30. in said second phase, guiding said flying body   (M) directly to said target (C).   18. Device according to claim 17, intended more particularly for the implementation of the specified method.   in any one of claims 3 to 9,   characterized in that said computing system (3) determines   said control charge factor (rco).   19. Device according to claim 17, intended more particularly for the implementation of the specified method.   according to any one of claims 10 to 14, characterized in that said computing system (3) determines   said longitudinal control plate (Oco).   Device according to claim 19, characterized in that said calculating system (3) determines,   in addition, said corrective acceleration (r2).   21. Device according to any one of claims 17   20, characterized in that said image sensor (2) is a Infrared radiation sensor.   22. Device according to any one of claims 17   20, characterized in that said image sensor (2) is a visible radiation sensor.