MOTOR-DRIVEN AIMING DEVICE AND METHOD†
The present invention relates to motor-driven aiming or steering of an element in a predetermined direction, and in particular to aligning a weapon on a line of sight.
STATE OF THE ART
It is known to mount an aiming device comprising a stationary structure and a steerable support on a weapon system that is steerable relative to a reference frame such as that of the vehicle carrying the weapon system if it is a motor-driven weapon system. The support of the aiming device is mounted on the structure of the weapon to be steerable about two axes of rotation, namely an elevation axis and a bearing axis, by means of two electric motors.
The motors are controlled so as to bring the steerable support into alignment on a direction corresponding to the line of sight determined by the sight setter of the weapon and so as to maintain the alignment.
When firing, the recoil of the weapon produces an impact that causes the support to turn suddenly. The motors are controlled to oppose this sudden turning until the control of the motors becomes saturated, thereby limiting the risk of damaging the electronics of the device, but making it impossible to maintain the alignment of the support on the line of sight. There then arises an offset between the real angular position of the support and the line of sight. The control of the motors does not enable the motors to take up this offset quickly, such that in the event of a burst of fire, there is a risk that the second shot and the subsequent shots will be further and further away from the target.

OBJECT OF THE INVENTION
An object of the invention is to provide means making it possible to improve the accuracy with which a motorized support is aligned in the event of an impact or any other physical phenomenon that leads to the motor becoming saturated.
BRIEF SUMMARY OF THE INVENTION
To this end, the invention provides a method of controlling an aiming device comprising a stationary structure having mounted thereon a support so as to be steerable about at least one axis of rotation by means of at least one motor, the support being provided with at least one inertial sensor of angular speed about that axis, the method comprising the steps of:
- servo-controlling the motor as a function of a difference between a nominal speed setpoint and a measurement of the angular speed sensor; and
- determining a correction value for correcting the nominal speed setpoint as a function of a difference between a reference inertial position and a current inertial position, and applying the correction value to the nominal speed setpoint.
In the event of the motor saturating, the reference inertial position is the position in which the support was to be found immediately prior to the motor saturating. This position is measured by the inertial sensor of angular speed. With the invention, the nominal speed setpoint is increased so as to bring the support quickly towards the reference inertial position.
The invention also provides an aiming device comprising a stationary structure having mounted thereon a support to be steerable about at least one axis of rotation by means of at least one motor connected to a control unit. The support is provided with at least one inertial sensor of angular speed about that axis, the control unit being arranged:

- to servo-control the control of the motor as a function of a difference between a nominal speed setpoint and a measurement of the angular speed sensor; and
- in the event of saturation being detected, to determine a correction value for correcting the nominal speed setpoint as a function of a difference between a reference inertial position and a current inertial position, and applying the correction value to the nominal speed setpoint.
Other characteristics and advantages of the invention appear on reading the following description of particular, non-limiting embodiments of the invention.
BRIEF DESCRIPTION OF THE FIGURES
Reference is made to the accompanying drawing, in which:
- Figure 1 is a diagrammatic view of an aiming device in accordance with the invention; and
- Figure 2 is a view showing diagrammatically how the motor of the aiming device is controlled.
DETAILED DESCRIPTION OF THE INVENTION
With reference to Figure 1, the aiming device of the invention comprises a stationary structure 1 in which there is mounted a support 2 to pivot about an axis 3, which is vertical in this example. The structure 1 is arranged to be secured on a carrier, e.g. a vehicle or a tank turret. The support 2 is arranged to carry the element that is to be aimed, a weapon or an aiming device, for example, and it is connected to the structure 1 by rolling bearings coaxial about the axis 3.
The angular position of the support 2 is adjustable about the axis 3 by means of an electric motor 4 having an outlet shaft connected via motion transmission means to a ring that is coaxial about the axis 3 and that is secured to the support 2. The motion transmission means may for example be gears, a belt, cables, … . The motor

may also be mounted to be directly engaged with the element that is to be driven, thereby connecting the structure 1 to the support 2.
The support 2 is also fitted with an inertial sensor for sensing angular speeds about the axis 3, namely a gyro 5.
The electric motor 4 and the gyro 5 are connected to a computer control unit 6 arranged to run a control program and including an interface enabling an operator of the aiming device to input data into the control program. The computer control unit 6 continuously stores the angular speed measured by the gyro 5.
The operation of the control program is illustrated in Figure 2 in the form of a control system given overall
reference 10 and arranged to control the electric motor 4
& as a function of a nominal speed setpoint θ calculated
from data input by the operator of the aiming device.
The control system comprises a main control loop 20 and a correction loop 30 that intervenes in the event of the electric motor 4 becoming saturated.
The main control loop 20 comprises a control element 21 for controlling motors that determines the control
parameters for the electric motor 4 as a function of a
& difference between a speed setpoint θ1 and a speed of the
&& support 2, written θM. The speed θM is measured by the
gyro 5.
The correction loop 30 comprises an estimator 31 for
estimating the difference between a reference inertial
position prior to saturation and a current inertial
position, and a corrector 32 that is arranged to correct
& the nominal speed setpoint θ as a function of the
difference. This correction is a correction of the
proportional integral type that supplies a corrected
& speed setpoint θC. The correction loop 30 also has a
detector 33 for detecting saturation of the electric
motor 4 on the basis of saturation information coming
from the control element 21. The detector 33 serves to

monitor the occurrence of saturation of the electric motor 4 and it is arranged to activate the correction
loop 30 in the event of the electric motor 4 saturating.
& A summing circuit 34 adds the nominal speed setpoint θ
& and the corrected speed setpoint θC in order to obtain
& the speed setpoint θ1.
Thus, in normal operation, when saturation does not
& occur, the speed setpoint θ1 is equal to the nominal
& speed setpoint θ.
In contrast, in the event of said saturation, the
correction loop 30 is activated by the detector 33 so
& that the nominal speed setpoint θ is corrected by the
corrector 32, which supplies the corrected speed setpoint
& θC.
Naturally, the invention is not limited to the embodiments described but encompasses any variant coming within the ambit of the invention as defined by the claims.
In particular, the support 2 may be mounted in the structure 1 so as to be adjustable in position about two mutually perpendicular axes, for example. The support 2 may be mounted in the structure 1 to be adjustable in elevation and in bearing relative to the structure 1 by means of two motors using either an inertial angle sensor having two sensing axes or else two inertial angle sensors each having one sensing axis.
The invention is applicable to any aiming device that is arranged to steer any element in a predetermined direction.
The support may be fitted with a plurality of inertial sensors: a first sensor used for the conventional stabilization control loop, and a gyro for the correction loop.
It is possible either to use an absolute reference position value, as mentioned above, or else to use the current absolute position error as calculated at each iteration of the control.

The method may be implemented continuously by adding an outer absolute (or inertial) position loop. The device for implementing the method then does not have elements for triggering and stopping the function 33; there is no reference measurement made by the estimator 31 and the speed setpoint supplied by the operator is always corrected by the speed setpoint from the corrector 32. This implementation serves to reduce considerably the impact of friction and also to increase performance in terms of stabilizing oscillations of the servo-controlled system. The method can thus also be used as a friction compensator.

CLAIMS
1. A method of controlling an aiming device comprising a
stationary structure having mounted thereon a support so
as to be steerable about at least one axis of rotation by
means of at least one motor, the support being provided
with at least one inertial sensor of angular speed about
that axis, the method comprising the steps of:
- servo-controlling the motor as a function of a difference between a nominal speed setpoint and a measurement of the angular speed sensor, and monitoring for the motor becoming saturated; and
- in the event of saturation being detected, determining a correction value for correcting the nominal speed setpoint as a function of a difference between a reference inertial position prior to the saturation and a current inertial position, and applying the correction value to the nominal speed setpoint.

2. A method according to claim 1, wherein the correction value is obtained by a correction of the proportional integral correction type.
3. An aiming device comprising a stationary structure having mounted thereon a support to be steerable about at least one axis of rotation by means of at least one motor connected to a control unit, the device being characterized in that the support is provided with at least one inertial sensor of angular speed about that axis, and in that the control unit is arranged:

- to servo-control the motor as a function of a difference between a nominal speed setpoint and a measurement of the angular speed sensor, and monitoring for the motor becoming saturated; and
- in the event of saturation being detected, to determine a correction value for correcting the nominal speed setpoint as a function of a difference between a reference inertial position prior to the saturation and a

current inertial position, and applying the correction value to the nominal speed setpoint.
4. A device according to claim 3, wherein the correction value is obtained via a correction of the proportional integral correction type.