Optronic sight having a critical mode, in particular an Anti-resonance mode, comprising a variable fundamental frequency, and motorised vehicle comprising such a sight

Abstract

The invention relates to an optronic sight having a critical mode, in particular an anti-resonance mode, comprising a variable fundamental frequency, and to a motorised vehicle comprising such a sight. This optronic sight for a motorised vehicle such as an aerial, marine or land vehicle, comprises: - a sighting module (13) capable of being moved about a first axis (X) and a second axis (Y) which is not parallel to the first axis; - means (14, 15) for moving the sighting module about the first axis and the second axis; and - a servo loop for slaving a position parameter of the sighting module to a setpoint, comprising an adaptive servo corrector (16) capable of calculating a command for a controlled device having a critical mode modifying the response of the device. The sight comprises means (23) capable of determining a fundamental frequency of the variable critical mode on the basis of an operating parameter of the controlled device, the corrector (16) being calculated from the fundamental frequency determined to compensate for the anti-resonance or resonance mode.

Description

[0001]DESCRIPTION TITLE: Optronic sight having a critical mode, in particular anti-resonance, comprising a variable fundamental frequency and a motorized vehicle comprising such a sight. Technical field of the invention: The present invention relates to the adaptive control of an optronic sight for a motorized vehicle such as an aerial, marine or land vehicle, that is to say, the control of such a sight which is capable of compensating for disturbances which affect the sight. Prior art: With reference to Figures 1 and 2, which illustrate an optronic sight 1 for a motorized vehicle and an operating diagram of such a sight according to the prior art, an optronic sight 1 comprises a sighting module 2 having a set of sensors, in particular cameras and / or pointing devices defining a line of sight Ldv of the optronic sight 1 corresponding to the optical axis exiting one of the sensors.The sighting module 2 is mounted on a support 3 attached to the motorized vehicle and can move along two axes, X and Y, under the action of movement means 4 and 5, which may include gimbals driven by motors controlled by control means 6. The purpose of the optronic sight 1 is to orient the line of sight Ldv towards a target regardless of the movements of the motorized vehicle and / or the target, and regardless of the environment and external disturbances (atmospheric conditions, etc.) or internal disturbances within the device. To this end, the sighting module 2 includes means for continuously measuring angular data 7, including a gyrometer for measuring angular velocity or a gyroscope for measuring the angular position of the line of sight Ldv. The carrier vehicle, through its movements or engine speeds, generates angular disturbances that impair the stability of the line of sight Ldv of the optronic sight 1.It is therefore necessary to implement a process to stabilize the image precisely and, in particular, to correct the speed or angular position of the line of sight Ldv. The viewfinder is thus equipped with a corrector 8 which receives the angular data measured by the measuring means 7 and which acts on the control means in order to compensate for the disturbances acting on the viewfinder 1. To reject the vibrational disturbances acting on the viewing module 2 and thus make the line of sight Ldv fixed in an inertial frame of reference, it is necessary that the sum of the torques, i.e. the motor torque Cmot, the torque due to the disturbances, and the friction torque Cf due to the gimbal bearings, applied to the viewing module 2 be zero. For this, as illustrated in Figure 2, it is conventionally known to use a servo loop 9 capable of acting on the angular data (speed or position) of the line of sight Ldv.Each block of said control loop 9 can be designed as a system, that is to say, a set of relationships linking inputs and outputs that can be made explicit using transfer functions. Reference may be made to document FR 3 130 023 which describes an example of adaptive control of an optronic sight capable of compensating for disturbances generated by an on-board device, such as a refrigeration machine, likely to affect the line of sight. The purpose of the control loop 9 is to allow the movement means 4 and 5 to generate a torque Cmot which compensates in particular for the friction torque Cf at the level of the motorized gimbals in order to stabilize the angular orientation of the line of sight, when a carrier vehicle carrying the sight moves angularly. As represented in Figure 2, the control loop 9 includes a digital part comprising a comparator 10 ensuring the comparison between a sampled measurement y. mkof the modeled angular data ym (position or angular velocity) of the line of sight and a reference yck to deliver a servo error ^^ to a linear and time-invariant controller K, and an analog part comprising transfer functions Hmot and Hcardan of the motor and gimbals, respectively, and a transfer function Hgyro modeling the dynamics of the measurement of the angular data (position or angular velocity) of the line of sight. The transfer function Hgyro is based either on the measurement y of the position of the line of sight obtained by a gyroscope, or on the measurement y of the angular velocity of the line of sight obtained by a gyrometer. The measurement of the modeled angular data of the line of sight y m then passes through an Analog-to-Digital Converter (ADC) and is thus sampled to deliver a sampled measurement y mkat comparator 10. The transfer function Hmot receives on the one hand an analog control voltage u corresponding to a digital control u k delivered by the corrector K and then converted by a Digital-to-Analog Converter (DAC) and, on the other hand, an analog voltage e corresponding to a back electromotive force feedback obtained from a back electromotive force constant Ke applied to the speed of movement Ω of the line of sight. The electromechanical torque Cmot supplied by the motor actuates the gimbals modeled by the transfer function H ca rd a n in order to compensate for or cancel the error ε kdue in particular to the perturbing friction torque Cf in the cardan shaft bearings. The software implementation of the compensator K is done as a combination (sum and / or product) of second-order digital linear filters. It is linear and time-invariant. The compensator K is also calculated to compensate for a mechanical mode C that appears in the mechanical transfer function. ^^^^^^and therefore a fortiori in the complete transfer function of the viewfinder between electrical voltage u and angular measurement y. The frequency of this anti-resonance mode varies with the system temperature T, but the controller, which is stationary, does not take this variation into account, which is likely to cause instability in the control system for significant temperature variations. Indeed, the gain of the mechanical transfer function between the useful torque and the gyrometric speed, as a function of frequency, is given by the Bode plot illustrated in Figure 3. The gain of the transfer function of a stationary speed controller between the gyrometric speed and the motor control voltage, as a function of frequency, is given by the Bode plot in Figure 4.The controller must therefore exhibit local amplification to compensate for the antiresonance present in the mechanical transfer function of the system to be controlled at the fundamental frequency fv of the antiresonance mode. However, the mechanical antiresonance mode exhibits significant frequency variability with temperature. A controller synthesized for a system at room temperature without considering the frequency variation le of the mechanical antiresonance mode is therefore completely unsuitable for extreme temperatures. Under these conditions, the control loop can become unstable. The variability of the antiresonance mode with temperature also affects the electrical transfer function via the back electromotive force feedback, which is itself proportional to the angular velocity of the transmission line. visée.Presentation of the invention The aim of the invention is therefore to overcome the aforementioned disadvantages and to propose an optronic sight for motorized equipment such as an aerial, marine or land vehicle, in which the performance of the servo loop remains optimal, despite the presence of a critical mode, in particular anti-resonance which appears in the servo mechanical system, this critical mode having a fundamental frequency which varies in the system to be servo.The invention therefore relates to an optronic sight for a motorized vehicle such as an aircraft, marine or land vehicle, comprising: - a sighting module capable of being moved around a first axis and a second axis not parallel to the first axis; - means for moving the sighting module around the first axis and the second axis; and - a servo loop for controlling a position parameter of the sighting module based on a setpoint, comprising an adaptive servo controller capable of calculating a command for a controlled device having a critical mode modifying the response of the device. The sight includes means capable of determining a fundamental frequency of the critical mode, which varies according to an operating parameter of the controlled device, the controller being calculated from the fundamental frequency determined to compensate for the critical mode. ri tique.A critical mode is defined as a mode that disturbs the response of the controlled device, such as a resonant or anti-resonant mode, at a natural frequency, when it is subjected to a control signal that involves amplification or, conversely, attenuation at that frequency. In one implementation, the fundamental frequency of the critical mode is variable depending on the temperature. The means for determining a fundamental frequency of the critical mode include a temperature sensor and a lookup table between temperature values ​​and fundamental frequency values.In another embodiment, the fundamental frequency of the critical mode is estimated as a function of the back electromotive force produced by the controlled device, based on a value representing the angular velocity of the aiming module. The means for determining a fundamental frequency of the critical mode include means for calculating a transfer function between the current supplying the controlled device and an output voltage of the controller. In various embodiments, the critical mode modifying the response of the device is a mechanical anti-resonance mode or, alternatively, a mechanical resonance mode. The servo-controlled position parameter of the aiming module can be the angular position of the aiming module or the velocity of the aiming module's movement. Advantageously, the adaptive controller includes a Linear Variable Parameter (LPV) controller. This adaptive controller can follow a state representation according to the following formula: where xk is the state variable of the controller, ^^ is the input control error of the adaptive controller, uk is the numerical control of the movement means calculated by the adaptive controller, f mi n and f max are two frequencies that bound the fundamental frequency in real time ^ ^ - ^ of the resonance or anti-resonance mode. Advantageously, the Linear Variable Parameter (LPV) controller includes the following affine state matrices: where A0, B0, C0, D0, A1, B1, C1, D1 denote matrix gains which are the parameters saved in the memory of said controller. In another embodiment, the optronic sight further includes means for acquiring the fundamental frequency of vibrational disturbances generated by the operation of at least one device of the sight, the adaptive controller being configured to receive said fundamental frequency of vibrational disturbances as input and to provide as output a displacement setpoint value to the displacement means based on said fundamental frequency and the fundamental frequency of the critical mode. In this embodiment, said adaptive controller advantageously follows a state representation according to the following formula: where xk is the state variable of the controller, ^ ^is the input control error of the adaptive controller, uk is the digital control of the means of movement calculated by the adaptive controller, fmi n and fmax are two frequencies bounding the fundamental real-time frequency ^^̂^ of the critical mode. For a two-parameter LPV controller, the state matrices (A, B, C, D) are affine in ^^̂^ and and are written in the form: ^^^^̂^, ^^̂^ = ^! + ^^̂^^^ + ^^̂^"^^^^̂^, ^^̂^ = ^! + ^^̂^^^ + ^^̂^"^^^^̂^, ^^̂^ = ^! + ^^̂^^^ + ^^̂^"^^^^^̂^, ^^̂^ = ^! + ^^̂^^^ + ^^̂^"where A0, B0, C0, D0, A1, B1, C1, D1, A2, B2, C2, D2 denote matrix gains which are the parameters saved in the memory of a software that implements said adaptive controller K( ^^̂^, ^^̂). The invention also relates to a motorized device such as an aerial, marine or land vehicle, comprising an optronic sight as defined above. Brief description of the figures Other objects, features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting examples, and made with reference to the accompanying drawings, in which: [Fig. 1] is a schematic view of an optronic sight according to the prior art; [Fig. 2] is a diagram representing the operation of an optronic sight according to the prior art; [Fig. 3] and [Fig.[Fig. 4] are Bode plots illustrating respectively the gain of the mechanical transfer function between the useful torque and the gyrometric speed as a function of frequency, and the gain of the transfer function of a stationary speed controller between the gyrometric speed and the motor control voltage as a function of frequency; [Fig. 5] is a schematic view of an optronic sight according to the invention; [Fig. 6] is a diagram representing the operation of an optronic sight according to the invention; [Fig. 7] is a schematic view of an optronic sight according to another embodiment of the invention; [Fig. 8] is a diagram representing the operation of the optronic sight of Figure 7; and [Fig. 9] is a diagram illustrating an optronic sight according to yet another embodiment of the invention. 10] is a diagram illustrating an optronic sight according to yet another embodiment of the invention.Detailed description of the invention: Reference is first made to Figures 5 and 6, which respectively represent an example of an embodiment of an optronic sight and an operating diagram of such a sight according to the invention. Such a sight is intended to equip an aerial vehicle, marine vehicle, or other type of vehicle, for example, an aircraft such as a helicopter.The optronic sight, designated by the general numerical reference 12, includes in particular: a sighting module 13 capable of being moved around a first X axis and a second Y axis, which may be non-perpendicular or perpendicular, respectively horizontal and vertical; means for moving the sighting module 13 around the first X axis and the second Y axis, consisting of motors controlled by commands C1 and C2 delivered by an adaptive controller 16; and means for continuously measuring angular data 17 representing the position of the sighting module 13 around the first and second axes, including a gyroscope, in the case of an angular position measurement, or a gyrometer, in the case of an angular velocity measurement. The measurement means deliver either angular position measurements θX and θY of the line of sight LdV of the sighting module 13, along the X and Y axes. Y, i.e., measurements of angular velocities Ω. X and Ω Yof the line of sight Ld V, along the X and Y axes. As in the prior art, the sighting module 13 is mounted on a support 18 fixed to the aerial, marine, or land vehicle. Referring to Figure 6, the optronic sight 12 includes a servo loop 20 for controlling a position parameter of the sighting module 13, in particular the absolute angular position θ X and θ Y or the absolute angular velocity Ω X and Ω Y of the line of sight Ld V along the X and Y axes on a position setpoint yc. This servo loop 20 includes a digital part comprising a comparator 21 ensuring the comparison between the setpoint y ck and a sampled measure y mkof the modeled angular data (position or angular velocity) of the line of sight to deliver a servo error Ɛk to the controller K). The analog part of the servo loop 20 includes the transfer functions Hmo t and Hca rd an of the motor and the cardan shafts, respectively, and the transfer function H g y ro modeling the dynamics of the measurement of the angular measurement data or velocity y of the line de visée. As in the embodiment described previously with reference to Figure 2, the measurement of the modeled angular data of the line of sight y m passes through an analog-to-digital converter (ADC) and is thus sampled to deliver a sampled measurement y mk to comparator 21. Similarly, the transfer function Hmo t receives, on the one hand, the analog control voltage u corresponding to a digital control uk delivered by the compensator then converted by a digital-to-analog converter (DAC) and, on the other hand, an analog voltage u e corresponding to the back electromotive force obtained from a back electromotive force constant Ke applied at the angular velocity Ω of the line of sight. The electromechanical torque C mo t supplied by the motor actuates the cardan shafts modeled by the transfer function H ca rd a n in order to compensate for or cancel the error Ɛ kdue to the disturbing frictional torque Cf in the cardan shaft bearings, but also a critical mechanical mode that appears in the transfer function Hcar ​​rd an. The critical mechanical mode is primarily an anti-resonance mode which, as previously indicated with reference to Figures 3 and 4, creates an attenuation in the transfer function of the controlled mechanical system, and in the overall transfer function of the controlled electromechanical system, including the cardan shafts and motors. However, we do not depart from the scope of the invention when the critical mode is a mechanical resonance mode of the controlled device which leads to an overvoltage in the electromechanical transfer function. In the following description, we will consider that the control system ensures compensation for the critical anti-resonance mode. As previously indicated, the frequency of the critical anti-resonance mode varies as a function of the temperature T. The controller K is linear and time-varying. It is configured to dynamically compensate for the anti-resonance mode included in the transfer function Hca rd an, which has a time-varying fundamental frequency. The control loop 20 thus includes means capable of determining the fundamental frequency ^ ^ - ^ of the anti-resonance mode comprising a temperature sensor 22 and a lookup table 23 in which fundamental frequency values ​​are stored as a function of temperature T. The lookup table 23 therefore receives, as input, a digital temperature value #k̂ resulting from sampling the measured temperature value T by an analog-to-digital converter (ADC). It delivers, as output, a fundamental frequency ^ ^ - ^corresponding to the temperature measured at the controller K, to deduce a digital control uk. From the fundamental frequency thus determined as a function of temperature, the controller is calculated to compensate for the anti-resonance mode. The calculations performed by the adaptive controller advantageously use Linear Variable Parameter (LPV) control. In the case of an LPV-controlled controller, a minimal state representation of the system K( ) is denoted by (A, B, C, D) with A The software state of the adaptive controller K( ^^̂^) is determined according to the following relationship: where xk∈ %^ is the state variable of the adaptive controller, ^^ is the input control error of the adaptive controller, uk is the digital command of the means of displacement calculated by the adaptive controller (output of the adaptive controller), fmi n and fmax are two frequencies bounding the real-time fundamental frequency ^^̂^ of the resonance or anti-resonance mode. For a single-parameter LPV controller, the state matrices (A, B, C, D) are affine in and are written under the forme : where A0, B0, C0, D0, A1, B1, C1, D1 denote matrix gains which are the parameters saved in the memory of a software program that implements said adaptive controller K( ^^̂^). Figures 7 and 8 show another embodiment of an optronic sight according to the invention. In these figures, elements identical to those described previously with reference to Figures 5 and 6 are designated by the same numerical references. In this embodiment, the means for determining the fundamental frequency of the anti-resonance mode include means for calculating 24 a transfer function g(U,I) between the current I supplying the controlled device, namely the motor 14 or the motor 15, and the digital electrical voltage U generated by the servo controller. The current is, for example, measured using a current sensor 25.The back electromotive force causes a perturbation in the overall transfer function, in particular in the transfer function of the motor Hmot, this back electromotive force being linked to the angular velocity of the line of sight, introducing an anti-resonance mode in the transfer function. The transfer function g(U,I) between the motor supply current and the digital output voltage ie of the controller thus makes it possible to identify in real time the fundamental frequency fv of the anti-resonance mode, which is provided to the adaptive controller to calculate the control voltage for the motors 14 and 15 driving the movement of the sighting module.The anti-resonance mode frequency can be identified either by finding a local minimum on a Fast Fourier Transform (FFT) or Power Spectral Density (PSD) ratio, or by identifying a transfer function via a recursive least squares method whose parameters allow the resonance frequency to be calculated. Finally, it should be noted that in the embodiments described above with reference to Figures 5 to 8, the LPV adaptive compensator is single-parameter, in that it is calculated from a fundamental frequency that compensates for the anti-resonance mode. This fundamental frequency depends on a parameter such as temperature, in the embodiment of Figures 5 and 6, or on the back electromotive force produced by the controlled device, in the embodiment of Figures 7 and 8, according to the angular position or the speed of movement of the aiming module.The corrector can, however, take several parameters into account. It can, in fact, consider the frequency of the mechanical anti-resonance mode, but also other sources of disturbances affecting the line of sight, whose natural frequency varies. For example, it could be a cooling system integrated into the optical sight, designed to cool the sighting module(s), and in particular, sighting modules that incorporate an infrared optical sensor requiring temperature control. A cooling system generates sinusoidal disturbances whose frequency varies according to the temperature required to cool the sighting module, which itself depends on the temperature of the external environment.In the embodiment illustrated in figures 9 and 10, which correspond respectively to a compensation of the disturbances produced by the back electromotive force feedback (figure 9) and to a compensation of the anti-resonance mode whose fundamental frequency varies as a function of temperature (figure 10), the digital control voltage uk is developed by the corrector from ir of the fundamental frequency of the anti-resonance mode ^. ^ - ^ and from the fundamental frequency vibrational disturbances generated by the operation of the device(s) 26 of the viewfinder causing the disturbances. The frequency of these sources of disturbances ^^̂^ and qui sont Independent and originating from different phenomena, they are acquired in parallel by distinct and independent means. The fundamental frequency Vibration disturbances can be provided via a communication module 27 to the computing means 24 (Fig. 9) or to the lookup table 23 (Fig. 10). In the case of a two-parameter LPV-controlled controller, a minimal state representation of the system K( , ) is denoted by (A, B, C, D) with A ∈ %^×^, B ∈ %^×^, C ∈ %^×^ and D ∈ %..of the adaptive controller adaptive, ^^ is the input control error of the adaptive controller, uk is the digital control of the movement means calculated by the adaptive controller (output of the adaptive controller), fmi n and fma x are two frequencies bounding the fundamental frequency in real time ^ ^ - ^ In the resonance or antiresonance mode, f'min and f'max are two frequencies bounding the fundamental frequency in real time. of the cold machine. For a two-parameter LPV-controlled compensator, the state matrices (A, B, C, D) are affine in ^^̂^ and and are written in the form: ^^^^̂^, ^^̂^ = ^! + ^^̂^^^ + ^^̂^"^^^^̂^, ^^̂^ = ^! + ^^̂^^^ + ^^̂^"^^^^̂^, ^^̂^ = ^! + ^^̂^^^ + ^^̂^"^^^^^̂^, ^^̂^ = ^! + ^^̂^^^ + ^^̂^" where A0, B0, C0, D0, A1, B1, C1, D1, A2, B2, C2, D2 denote matrix gains which are the parameters saved in the memory of a software that implements said adaptive controller K( ^^̂^, ^^̂). Finally, it should be noted that in the embodiments just described, the viewfinder includes a controller that is calculated so as to compensate for the anti-resonance mode of the controlled device. As indicated previously, the invention also applies to the compensation of a mechanical resonance mode of the controlled device which leads to an overvoltage in the electromechanical transfer function and therefore by integrating an anti-resonance into the servo controller.In the case of compensation for a mechanical resonance mode, a determination of the fundamental frequency of the resonance mode is similarly made, the corrector being calculated from the fundamental frequency determined to compensate for the resonance mode.

Claims

CLAIMS 1 Optronic sight for motorized equipment such as an aerial, marine or land vehicle, comprising: - a sighting module (13) capable of being moved around a first axis (X) and a second axis (Y) not parallel to the first axis; - means (14, 15) for moving the sighting module around the first axis and the second axis; and - a servo loop (20) for controlling a position parameter of the sighting module on a setpoint, comprising an adaptive servo controller (16) capable of calculating a command (CI, CII) for a controlled device having a critical mode modifying the response of the device, characterized in that it comprises means (22, 23; 24, 25) capable of determining a fundamental frequency ( ^^̂^) of the critical mode which varies according to an operating parameter of the controlled device, the controller being calculated from the fundamental frequency determined to compensate for the critical mode.

2. Optronic sight according to claim 1, wherein the fundamental frequency of the critical mode is variable as a function of temperature, the means for determining a fundamental frequency of the critical mode comprising a temperature sensor (22) and a lookup table (23) between temperature values ​​and fundamental frequency values.

3. Optronic sight according to claim 1, wherein the fundamental frequency. The critical mode is estimated via the back electromotive force produced by the controlled device, as a function of a data point representing the angular velocity of the aiming module. The means for determining a fundamental frequency of the critical mode include means (24) for calculating a transfer function between the current supplying the controlled device and an output voltage of the corrector.

4. Optronic sight according to any one of claims 1 to 3, wherein the critical mode modifying the response of the device is a mechanical anti-resonance mode.

5. Optronic sight according to any one of claims 1 to 3, wherein the critical mode modifying the response of the device is a mechanical resonance mode.

6. Optronic sight according to any one of claims 1 to 5, wherein the servo-controlled position parameter of the aiming module is the angular position of the aiming module (13).

7. Optronic sight according to any one of claims 1 to 5, wherein the servo-controlled position parameter of the sighting module is the velocity of the sighting module's movement (13).

8. Optronic sight according to any one of claims 1 to 7, wherein the adaptive controller comprises a Linear Variable Parameter (LPV) controller.

9. Optronic sight according to claim 8, wherein said adaptive controller (16) follows a state representation according to the following formula: where xk is the state variable of the controller, ^^ is the input control error of the adaptive controller (16), uk is the digital control of the means of displacement calculated by the adaptive controller (16), fmi n and fmax are two frequencies bounding the fundamental real-time frequency^^̂^ of the critical mode.

10. Optronic sight according to claim 8 or 9, wherein said Linear Variable Parameter (LPV) corrector comprises the following affine state matrices: where A0, B0, C0, D0, A1, B1, C1, D1 denote matrix gains which are the parameters saved in memory of said controller.

11. Optronic sight according to any one of claims 1 to 8, further comprising means for acquiring the fundamental frequency of vibration disturbances generated by the operation of at least one device (26) of the sight, the adaptive controller being configured to receive as input said fundamental frequency of vibration disturbances ( ) and to provide as output a displacement setpoint value to the displacement means based on said fundamental frequency of vibration disturbances and the fundamental frequency of the critical mode ( ).

12. Optronic sight according to claim 11, wherein said adaptive controller (16) follows a state representation according to the following formula: where xk is the state variable of the controller, ^^ is the input control error of the adaptive controller (16), uk is the digital control of the means of movement calculated by the adaptive corrector (16), f mi n and f max are two frequencies that bound the fundamental frequency in real time of the critical mode.

13. Optronic sight according to claim 12, wherein said Linear Variable Parameter (LPV) corrector comprises the following affine state matrices where A0, B0, C0, D0, A1, B1, C1, D1, A2, B2, C2, D2 denote matrix gains which are the parameters saved in memory of said corrector.

14. Motorized device such as an aerial, marine or other vehicle, comprising an optronic sight according to any one of claims 1 to 13.

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