EP1291600B1 - Method for guiding a device, especially a munition - Google Patents

Description

The subject of the present invention is a method of guiding a gear towards a target, in particular to improve the accuracy of the shooting of a Ammunition previously calculated to reach the target.

DE 35 22 154 is mentioned as prior art.

To launch an artillery ammunition, including ammunition barrel or mortar, the position of the target target is provided before firing to a fire calculator determining values of fire parameters like the angles of the shot and the initial speed to be transmitted to the ammunition when firing. After the shot and in the absence of guidance, the ammunition follows a trajectory ballistic.

The assumptions made during the fire calculation differ from the actual conditions of fire and theft of the ammunition. So for example the mass the actual ammunition or its distribution in the ammunition volume is slightly different, within the limits of the manufacturing tolerances of the ammunition, mass or mass distribution taken into account in the calculation of the shot. In addition, wind conditions can change significantly during flight time. Differences between assumptions and conditions real lead to a real impact point of the ammunition distinct from the point impact initially planned on the target.

The impact accuracy of the ammunition is better when the gap between the actual point of impact and the planned point of impact is reduced and the guns or current mortars equipped with their fire calculator ensure accuracy relatively good impact. For example a mortar with a shell and draws from the front presents a curved shot with a range of less than 15 kilometers and a precision of a hundred meters. A gun is loaded to the back and makes a more horizontal shot with a range of up to 40 kilometers. However the more important and frequent imbrication of the forces adversaries and the presence of civilian populations impose the need for the artillery to be able to operate further destruction and neutralization more precise by firing a munition and guiding it on its flight to a well defined target.

The guiding of a munition is carried out in a known manner by placing implementation of a guide law on all or part of the flight of the ammunition. The law The guide system determines instructions to be applied to an actuator of the munition, for example an impeller or a group of control surfaces, for modify the trajectory of the ammunition during its flight in order to bring it closer of the target.

Proportional navigation is a known guide law of a ammunition which consists in controlling a proportional charge factor to the rotation speed of the line connecting the ammunition to the target. This speed being for example measured using homing devices carried by the ammunition or calculated from parameters provided for example by a central inertial embedded in the ammunition. Load factor control peculiar to proportional navigation leads to a rotational speed from the line connecting the ammunition to the target tending toward zero. Navigation Proportional tends to collide the guided munition with the target. This guidance makes it possible to null the distance of passage which is the distance between the point of real impact and the target.

Proportional navigation guidance is easy to implement it has the disadvantage of imposing a rectilinear trajectory on the ammunition that is not optimal with respect to the curved ballistic trajectory that follows a munition without guidance.

The problem is to develop a guidance of the ammunition ensuring like proportional navigation a passing distance theoretically zero but with a lower load factor. It's about to find guidance with impact accuracy as good as the one obtained with proportional navigation guidance while presenting a lower energy cost.

The invention responds to this problem by a guiding method of a machine, in particular a munition, towards a target, the method applying to the machine a proportional acceleration proportional to the vector product of the speed of the machine by the difference of the vectors rotation of the connecting line the craft and the target and the right connecting the craft to the point of ballistic impact predicts said craft.

le procédé effectue une mesure de la position courante M de ladite munition à l'instant t et de son vecteur vitesse courant V _M,

le procédé calcule par prédiction de trajectoire le point d'impact balistique I correspondant à la position courante M de ladite munition,

le procédé estime le vecteur rotation munition-impact Ω _MI de la droite reliant la munition M au point d'impact balistique I,

le procédé calcule le vecteur rotation munition-cible Ω _MB de la droite reliant la munition M à ladite cible B,

le procédé calcule une accélération Γ _c de consigne proportionnelle et de signe inverse au produit vectoriel du vecteur vitesse V _M de la munition par la différence entre le vecteur rotation munition-impact Ω _MI et le vecteur rotation munition-cible Ω _MB soit Γ c = - K V M Λ (Ω MB - Ω MI)

   où K est un coefficient strictement supérieur à 2,More particularly, the method comprises for example the following steps:

the method makes a measurement of the current position M of said munition at time t and of its current speed vector V _M ,

the method calculates by trajectory prediction the point of ballistic impact I corresponding to the current position M of said munition,

the process estimates the ammunition-impact rotation vector Ω _MI of line joining ammunition M to ballistic point of impact I,

the process calculates the rotation vector ammunition-target Ω _MB of the line connecting the munition M to said target B,

the process calculates an acceleration Γ _c of proportional setpoint and inverse sign to the vector product of the velocity vector V _M ammunition by the difference between the ammunition-impact rotation vector Ω _MI and the ammunition-target rotation vector Ω _MB be Γ vs = - K V M Λ ( Ω MB - Ω MID )

where K is a coefficient strictly greater than 2,

The guidance according to the process starts for example after the climax the trajectory of the ammunition fired. The process is iterative in closed loop for example until the impact of the ammunition, or to a position of the ammunition providing significantly better impact accuracy than obtained with unguided ballistic fire.

The method generates guiding orders carrying out a navigation proportional change around the ballistic trajectory of the munition. The guide law of the method according to the invention allows the munition thus guided to move towards the target by deviating slightly from its ballistic trajectory. The implementation of the method according to the invention has the advantage of requiring a low load factor.

• la figure 1, un exemple d'asservissement classique d'une consigne d'accélération appliquée à une munition ;
• la figure 2, un exemple d'asservissement d'une consigne de position appliquée à une munition ;
• la figure 3, un exemple de trajectoire avec et sans l'invention.

Other characteristics and advantages of the invention will become apparent with the aid of the following description made with reference to appended drawings which represent:

• FIG. 1, an example of conventional servocontrol of an acceleration instruction applied to a munition;
• FIG. 2, an example of servocontrol of a position command applied to a munition;
• FIG. 3, an example of a trajectory with and without the invention.

FIG. 1 schematically illustrates a conventional servocontrol of an acceleration instruction applied to a munition. After the shot and during its flight, the ammunition no longer follows its ballistic trajectory but is guided by means of a command of its transverse acceleration vector. A guidance calculator 1 generates from the information represented by the inputs X1 to Xn a guiding order for controlling the transverse acceleration vector of the munition 8 in the form of a vector value. γ _c acceleration setpoint. This instruction γ _it is compared in a comparator 2 to vector transverse acceleration γ measured _m of the ammunition 8 using an instrument case 3 comprising gyrometers and accelerometers. The gap 4 between the commanded acceleration γ _c and measured acceleration γ _m is introduced into a compensating calculator 5, which generates, starting from particular current rotation angles of the ammunition and the gap 4, a position command δ of a rudder of the ammunition whose purpose is to reduce the difference between the measurement and the instruction. On the aerodynamic cell represented by the ammunition 8, the position command δ is executed for example by means of a signal amplifier 6 followed by a steering motor 7. The reactions of the ammunition 8 to the position command δ are measured using the instrument box 3 and again compared to the setpoint γ _c acceleration so as to achieve a closed loop servo to the set value provided by the guidance computer.

Figure 2 schematically shows a servo a position instruction applied to a munition containing a embedded inertial unit. A position command 30 to be reached by a munition 23 is supplied as input to a guidance calculator 21 which also receives as input measures 25 from an inertial unit 22 on the munition 23. The guidance computer 21 implement a guiding algorithm elaborating from the inputs of the calculator a load factor value 24 to be applied to the cell aerodynamic represented by the ammunition 23 to change the trajectory so that it satisfies said position instruction provided at the input of the guidance computer 21. The load factor is a acceleration developed laterally to change the ammunition of path. The guidance algorithm makes it possible to control an acceleration respecting a guide law. The onboard inertial unit 22 is example, a hybridized GPS inertial unit, whose abbreviation stands for Global Positionning System in English, with accelerometers and gyrometers, and to calculate the coordinates of the position, the components of the speed and attitudes of the ammunition. The power plant embedded inertial 22 makes 25 measurements of the flight situation of the munition which feed the guidance computer 21 in a loop of guidance which is a closed loop servo.

The load factor value 24 is applied to the ammunition 23 by means of a control computer 26 receiving as input the value of load factor 24 on the one hand and measures 27 on the actual movement of the ammunition subjected to the load factor 24 that come from the central inertial 22 boarded on the other hand. The piloting computer 26 elaborates a steering value 28 which is applied to the actuators 29 which influence on the flight path and orientation of the ammunition. A control loop is closed between the control computer 26 and the ammunition 23 by the introduction in the control computer 26 of new measures 27 of the flight situation of the ammunition, for example acceleration variations and rotation captured by the accelerometers and gyrometers of the plant inertial 22 boarded. The control loop ensures the enslavement of the ammunition 23 at the load factor value 24 recorded.

The activation of the guidance and steering loops assures the guiding the ammunition. Guiding can be carried out on all or part of the ammunition race.

Figure 3 shows two trajectories of a munition. To aim a target, or goal, B of known position, a munition M is drawn for example from a point O with a conventional preliminary fire calculation determining the firing angles and the initial speed to apply to the munition based assumptions about values such as the mass of the munition, aerodynamic characteristics of the munition and a known wind condition or predicts. After firing, the ammunition describes a real trajectory 31 and reaches at a certain date t a point M, for example located after the apogee 32 of the path. Various deviations from the assumptions taken into account during of the shot lead the ammunition to travel a real trajectory 31 different from the ballistic trajectory 30 provided during the firing.

If the ammunition is not guided, it is subjected to a ballistic acceleration Γ _TP due mainly to the forces of gravity and drag corresponding to the aerodynamic slowdown, and from the point M it follows a ballistic trajectory whose estimate at time t is a first ballistic trajectory that does not reach the target B but presents a ballistic impact point 1 whose position in space is distinct from that of the target.

The implementation of the guiding method according to the invention leads to the ammunition to perform a second trajectory 34 which reaches the target.

The ammunition is controlled by a position command whose value is that of the position of the target B. The enslavement is for example the one described with reference to FIG. 2 and implements a guiding law according to the invention. The munition is for example equipped with an inertial unit hybridized GPS that calculates the coordinates of position M and the components of ammunition velocity as well as the attitudes of the ammunition.

From the point M and in the absence of guidance control, the ammunition trajectory is ballistic and has an impact point I with the ground.

At the instant t, the ammunition, animated by the speed V _M , is located at the position M. The inertial hybridised GPS onboard unit calculates the speed V _M and the position M for example by the calculation of the vector OM between the point O of origin of the shot and the position M.

The coordinates of the point of ballistic impact I are for example evaluated by prediction in a landmark by simplified simulation of the ballistic trajectory Π from the point M of the munition at time t in integrating the state vector until the impact l.

In a temporal landmark of variable τ, the ballistic trajectory préd predicted at time t has a current point P (t, τ) depending on the time t during which the munition is at position M. The current point P (t , τ) is animated by a speed V _p (t, τ) also dependent on t and the variable τ to describe the predicted ballistic trajectory Π.

In the simplified simulation of the ballistic trajectory Π, the derivatives V ˙ _x , V ˙ _y and V ˙ _z with respect to the time τ of the components V _x , V _y and V _z of the velocity vector V _p (t, τ) on a terrestrial reference (O, x, y, z) are expressed by the following relations: V x = - q S Cx V x m V V there = - q S Cx V there m V V z = - q S Cx V z m V + g where g is the acceleration of gravity,
V is the speed module V _p (t, τ) equal to the square root of the sum of the squares of the components V _x , V _y and V _{z of} said velocity vector V _p (t, τ),
q is equal to 1/2 ρ V ² where ρ is the density of the air,
S is the surface of the master torque of the ammunition,
Cx is the drag coefficient of the ammunition and
m is the mass of the ammunition.
Said components V _x , V _y and V _z are the derivatives with respect to the time τ of the components in said terrestrial frame (O, x, y, z) of the current point P (t, τ).

After estimating the point of impact 1, the method of the invention evaluates the rotation Ω _MI to which the vector is subject MID , called rotation of the right ammunition-impact Ml, according to the following expression: Ω MID = - MID Λ V M r l 2 according to which the rotation vector Ω _MI is equal to the opposite of the vector product of the vector MID connecting the ammunition to its ballistic impact by the ammunition velocity vector V _M , which vector product is divided by the square of the distance r ₁ between the position M of the munition and the position 1 of the point of ballistic impact I corresponding to said position M.

From any position M of the munition whose coordinates are for example calculated from the point O of origin of the shot and with the aid of the GPS hybridized inertial unit embedded in the munition, and the known position of target B, the guiding method according to the invention evaluates the rotation Ω _MB to which the vector is subject MB called the rotation of the straight line munition-target MB, for example using the following vector relationship: Ω MB = MB Λ ( V B - V M ) r 2 according to which the rotation vector is equal to the vector product of the vector MB connecting the ammunition to the target by the difference of the velocity vector of the target V _B and the speed vector of the ammunition V _M , which vector product is divided by the square of the distance r between the position M of the munition and the position B of the target.

In the particular example of FIG. 3, the speed of the target is zero and the expression of the ammunition-target rotation Ω _MB is simplified accordingly. The expression of Ω _MB is then the following: Ω MB = - MB Λ V M r 2 in which the data of the onboard GPS hybridised inertial unit allow the calculation of the three terms MB , V _M and r.

In all cases, the guiding method according to the invention controls a setpoint acceleration Γ _c on ammunition at point M whose value is proportional to the vector product of the ammunition velocity V _M by the difference of the rotation vector Ω _MB of the line connecting the ammunition and the target and the rotation vector Ω _MI of the straight line connecting the ammunition to the point of ballistic impact I predicted for said munition from its known position in point M. Either the following guidance law: Γ vs = - K V M Λ ( Ω MB - Ω MID ) where K is a coefficient of proportionality.
K is strictly greater than 2.

A value of K strictly greater than two ensures a stability of the guide servo. The value of the coefficient of proportionality K is preferably limited to a value between three and four.

In the example of FIG. 3, the munition is equipped with a GPS hybridized inertial unit, which comprises three accelerometers and three gyrometers, and the setpoint acceleration vector. Γ _c is calculated in terrestrial axes for example in said reference (O, x, y, z). The vector Γ _it is projected on the axes of the munition, in which the actuators of the munition operate, by the rotations ψ,  and φ measured by the inertial unit. The rotations ψ,  and φ correspond to the passage of the terrestrial trihedron (x, y, z) to the trihedron of the axes of pitch, yaw and roll of the munition.

The method of the invention controls an acceleration perpendicular to the speed of the ammunition. The obliqueness of which the measured value the angle between the longitudinal axis, or roll axis, of the munition and the vector velocity of the ammunition present in the flight phase of the ammunition a value less than a few degrees. The setpoint acceleration according to the invention advantageously has a substantially zero projection on the roll axis of the ammunition.

In an alternative embodiment of the invention, the munition is not equipped with a GPS hybridized inertial unit, but it is equipped with a GPS receiver, two accelerometers for generating control commands for the actuators, and a gyrometer. The GPS receiver provides measurements in a reference pseudo-aerodynamic trihedron. The target acceleration vector Γ _c according to the invention is projected on said pseudo-aerodynamic trihedron by the rotations of aerodynamic azimuth χ and aerodynamic slope γ, which are calculated using the components of the speed of the ammunition V _M expressed in terrestrial axes, and by the rolling rotation of the munition φ measured by said gyrometer. The yaw and pitch angles of the munition are respectively assimilated to, or modeled by, the azimuth and slope angles of the velocity vector provided by the GPS receiver. This variant has the advantage of leading to a lighter ammunition than in the example of FIG.

In another variant of the invention differing from the example of FIG. 3 by a value of the target speed vector V _B non-zero, rotation Ω _MB to which the vector is subject MB , called rotation of the right-munition-target MB, is measured by means of a homing device equipping the munition. The on-board autodirector comprises a target detection system B and calculation means or mechanical means for estimating the rotational speed Ω _MB of the right ammunition-target. In this variant, the ammunition includes an onertial unit and an onboard self-steering. This variant has the advantage of being free of knowledge of the speed of the target.

The calculation of the setpoint acceleration Γ _c according to the guide law of the invention is iterated by the method according to a temporal sampling which depends on the dynamic response of said munition to a load factor. The method is for example implemented with a sampling of 20 Hertz for a 120 millimeter mortar ammunition.

The second trajectory 34 of FIG. 3 has the advantage of being curve. It is at every moment close to the ballistic trajectory instant ammunition. The guide path according to the method of the invention differs from the guidance according to the proportional navigation classic that imposes a rectilinear trajectory to the ammunition. Navigation In particular, the proportional method tends to make the guidance trajectory lower than that of the natural ballistics of the ammunition, this lower trajectory to be compensated at the end of the guidance by a trajectory higher than the ballistic trajectory. Navigation proportional leads over time to commands from an actuator ammunition that are a bit contradictory and are not optimal.

When the ballistic impact point 1 coincides with the position of the target B, the guidance according to the invention has the particular advantage of controlling a setpoint acceleration Γ _c zero, it does not perform trajectory error correction when the ballistic trajectory reaches the target. Proportional navigation in such a case a course correction which corresponds to a degradation compared to natural ballistics.

The guidance according to the invention allows a cost in energy, a size and a reduced mass of ammunition.

The method according to the invention provides the control of a factor of zero final charge. At the end of the guide according to the invention, the speed of the ammunition has the advantage of being aligned with its longitudinal axis during the impact. The invention makes it possible to optimize the terminal efficiency of the load of the ammunition.

The method according to the invention has been described for an application to guiding a munition. It applies of course also to other types gear to guide to a target.

Claims (12)

1. Method for guiding a device towards a target, characterized in that it applies to the device (M) a preset acceleration proportional to the vector product of the velocity of the device (M) times the difference of the rotation vectors of the straight line joining the device (M) and the target (B) and of the straight line joining the device to the predicted point of ballistic impact of the said device.
2. Method according to Claim 1, characterized in that it comprises at least the following steps:

   the method performs a measurement of the current position M of the device at the instant t and of its current velocity vector V _M on the basis of sensors,

   the method calculates by prediction of trajectory the point of ballistic impact I corresponding to the current position M of the device,

   the method calculates the device/impact rotation vector Ω _MI of the straight line joining the device M to the point of ballistic impact I,

   the method estimates the device/target rotation vector Ω _MB of the straight line joining the device M to the said target B,

   the method calculates a preset acceleration Γ _c proportional and of inverse sign to the vector product of the velocity vector V _M of the device times the difference between the device/impact rotation vector Ω _MI and the device/target rotation vector Ω _MB i.e. Γ c = - K V M Λ ( Ω MB - Ω MI) where K is a coefficient strictly greater than 2,

   the method applies the preset Γ _c as acceleration to the device.
3. Method according to Claim 2, the method being characterized in that the said coefficient K lies between 3 and 4.
4. Method according to any one of the preceding claims, characterized in that it is iterated in a closed loop.
5. Method according to Claim 3, characterized in that it is iterated in a closed loop up to impact.
6. Method according to any one of the preceding claims, characterized in that it carries out a sampling of the preset acceleration which depends on the response dynamics of the device.
7. Method according to any one of the preceding claims, characterized in that the device exhibiting a pitch axis, a yaw axis and a roll axis, the preset acceleration Γ _c is projected onto the pitch and yaw axes of the device and is substantially zero on the roll axis.
8. Method according to one of the preceding claims, characterized in that the device exhibiting a pitch axis and a yaw axis and being equipped with a GPS receiver, the angles of yaw and of pitch of the device are respectively akin to the angles of azimuth and of slope of the velocity vector of the device.
9. Method of guidance according to one of Claims 1 to 7, characterized in that the device being equipped with a GPS hybridized inertial platform measuring at least three rotations ψ,  and , the preset acceleration vector Γ _c calculated in terrestrial axes is projected onto the axes of the device by the said three rotations.
10. Method according to any one of the preceding claims, characterized in that the target being assumed to have zero velocity, the device/target rotation vector Ω _MB is calculated.
11. Method according to any one of the preceding claims, characterized in that the device comprising a seeker, the device/target rotation vector Ω _MB is estimated by the seeker.
12. Method according to any one of the preceding claims, characterized in that the device is a munition.

Images