FR3157565A1 - Cassegrain telescope with piezoelectric actuators for high-performance gyro-stabilized viewfinder - Google Patents

Abstract

Telescope (1), comprising: - a primary mirror (10) mounted on a support (11), - a secondary mirror (20), - an articulated structure (40) arranged between the support (11) and the secondary mirror (20) to allow six degrees of freedom of the secondary mirror (20) relative to the primary mirror (10), - a plurality of piezoelectric actuators (50) mounted to move the secondary mirror (20) by acting on the articulated structure (40), - at least one sensor (70) for aligning the primary mirror (10) and the secondary mirror (20), - an electronic processing unit electrically connected to the actuators and arranged to control the actuators (50) so as to maintain alignment between the primary mirror (10) and the secondary mirror (20). ABRIDGED FIGURE: Fig. 1

Description

Cassegrain telescope with piezoelectric actuators for high-performance gyro-stabilized viewfinder

The present invention relates to the field of optical devices, for example intended for aiming. More specifically, the present invention relates to the field of high-precision gyro-stabilized sights applied to on-board systems.

BACKGROUND OF THE INVENTION

Gyro-stabilized sights are known from the state of the art that can be used to form optronic devices commonly referred to as gyro-stabilized balls. In a manner known per se, a gyro-stabilized ball comprises a photosensitive sensor, optical elements carried by a mechanical structure to define an optical path to the photosensitive sensor, and an electronic processing unit connected to the photosensitive sensor to process the signals from said sensor.

In a stressed environment (severe vibrations, thermal gradients and/or load factor), the mechanical structure supporting the optical elements can deform and alter the optical path. For example, in a telescope, the mechanical structure supports two mirrors facing each other, thus defining the optical path between them. When a deformation of the mechanical structure occurs, the optical path itself is then deformed.

Thus, to meet the objectives of improving the image quality of the optronic chain, a current solution consists of further stiffening the mechanical structure.

Unfortunately, such a mechanical structure is particularly expensive and is accompanied by difficulties in manufacturing or configuring the position and orientation of one mirror relative to the other. In addition, the use of the same material is necessary throughout the telescope in order to limit deformations linked to differential expansion and the thermal gradient, since the temperature is not uniform across the entire mechanical structure.

SUBJECT OF THE INVENTION

The invention aims in particular to remedy at least in part the aforementioned drawbacks.

For this purpose, according to the invention, a telescope is provided comprising:

- a primary mirror mounted on a support,

- a secondary mirror,

- an articulated structure which is arranged between the support and the secondary mirror to allow six degrees of freedom of the secondary mirror relative to the primary mirror,

- a plurality of piezoelectric actuators mounted to move the secondary mirror by acting on the articulated structure,

- at least one sensor of an alignment of the primary mirror and the secondary mirror,

- an electronic processing unit electrically connected to the actuators and arranged to control the actuators so as to maintain alignment between the primary mirror and the secondary mirror.

Thus, a new telescope architecture is advantageously proposed. The chosen architecture allows the secondary mirror to be permanently aligned with respect to the said primary mirror. Indeed, the sensor detects a misalignment or deformation of the secondary mirror with respect to the primary mirror. The information is then received by the electronic processing unit which controls the piezoelectric actuators in order to realign the secondary mirror and the primary mirror.

• le télescope comprenant une couronne secondaire montée autour du miroir secondaire et reliée par une armature à la structure articulée ;
• l’armature comprend trois bras qui sont agencés sensiblement en triangle tangentiellement à la couronne secondaire et qui ont chacun deux extrémités, les bras sont fixés deux à deux par leurs extrémités formant un sommet du triangle, les sommets étant fixés à la structure articulée ;
• la structure articulée comprend trois paires de jambes, les jambes de chaque paire ayant des premières extrémités écartées l’une de l’autre et reliées chacune au support par l’intermédiaire d’un des actionneurs piézo-électriques, et des deuxièmes extrémités rapprochées l’une de l’autre et reliées à l’un des sommets de l’armature ;
• la première extrémité de chacune des jambes est reliée à l’actionneur piézo-électrique par une première liaison sphérique et la deuxième extrémité est reliée à l’armature par une deuxième liaison double pivot, les deux liaisons étant agencées pour autoriser une rotation de l’armature par rapport au support ;
• chacun des actionneurs piézo-électriques est agencé pour produire un mouvement de translation selon une direction longitudinale de la jambe à laquelle il est relié ;
• les actionneurs piézo-électriques sont attenants au support ;
• le capteur est un capteur sans contact porté par un bâti surmontant le support et agencé pour détecter une position d’une cible solidaire du miroir secondaire ;
• le capteur sans contact est un capteur de position inductif, ou capacitif ou à courants de Foucault ;
• l’unité électronique pilote les actionneurs en fonction d’une loi de commande agencée pour maintenir l’alignement entre le miroir primaire et le miroir secondaire.

According to optional features, used individually or in whole or in part in combination:

• the telescope comprising a secondary crown mounted around the secondary mirror and connected by a frame to the articulated structure;
• the frame comprises three arms which are arranged substantially in a triangle tangentially to the secondary crown and which each have two ends, the arms are fixed two by two by their ends forming a vertex of the triangle, the vertices being fixed to the articulated structure;
• the articulated structure comprises three pairs of legs, the legs of each pair having first ends spaced apart from each other and each connected to the support via one of the piezoelectric actuators, and second ends close to each other and connected to one of the vertices of the frame;
• the first end of each of the legs is connected to the piezoelectric actuator by a first spherical connection and the second end is connected to the armature by a second double pivot connection, the two connections being arranged to allow rotation of the armature relative to the support;
• each of the piezoelectric actuators is arranged to produce a translational movement in a longitudinal direction of the leg to which it is connected;
• the piezoelectric actuators are attached to the support;
• the sensor is a contactless sensor carried by a frame surmounting the support and arranged to detect a position of a target secured to the secondary mirror;
• the non-contact sensor is an inductive, or capacitive or eddy current position sensor;
• The electronic unit controls the actuators according to a control law arranged to maintain alignment between the primary mirror and the secondary mirror.

Other characteristics and advantages of the invention will emerge upon reading the following description of a particular and non-limiting embodiment of the invention.

Reference will be made to the attached drawings, including:

FIG. 1 there FIG. 1 is a perspective view of a telescope, according to the invention;

FIG. 2 there FIG. 2 is a front view of the telescope shown in FIG. 1 ;

FIG. 3 there FIG. 3 is a top view of the telescope shown in FIG. 1 ;

FIG. 4 there FIG. 4 is a perspective view of an element of the telescope according to the invention;

FIG. 5 there FIG. 5 is a representation of the telescope provided with sensors according to the invention;

FIG. 6 there FIG. 6 is a top view of the sensor-equipped telescope shown in FIG. 5 ;

FIG. 7 there FIG. 7 is a front view of the sensor-equipped telescope shown in FIG. 5 ;

FIG. 8 there FIG. 8 is a functional diagram of a control law according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference to figures 1 to 8, a telescope 1 is described according to a particular embodiment of the invention.

The telescope 1 is here a Cassegrain type telescope and comprises a primary mirror 10 mounted on a support 11 and a secondary mirror 20 arranged to be opposite the primary mirror 10.

The primary mirror 10 comprises a concave reflecting upper surface and a lower surface, opposite the upper surface and carried by the support 11. The primary mirror 10 comprises a central hole having a central axis X extending orthogonally to said lower surface. In a manner known per se, a photosensitive sensor is intended to be positioned opposite the central hole, perpendicular to the central axis X.

The support 11 has an upper surface 11.1 facing said lower surface of the primary mirror 10, and a lower surface opposite the upper surface 11.1. The upper surface 11.1 is connected to said lower surface of the primary mirror 10 by means of studs known per se and arranged to fix the primary mirror 10 to the support 11 while limiting as much as possible the constraints on the primary mirror 11.

The secondary mirror 20 comprises a convex reflective lower surface and an upper surface, opposite said lower surface. In addition, the secondary mirror 20 also comprises a cylindrical peripheral surface. The secondary mirror 20 has a central axis aligned with the central axis X of the primary mirror 10 to define an optical axis of the telescope 1. The central axis of the secondary mirror 20 is therefore coincident with the central axis X previously defined.

A secondary crown 21 matches the shape of the cylindrical peripheral surface of the secondary mirror 20. In other words, the secondary crown 21 encircles the secondary mirror 20.

The telescope 1 also comprises a frame 30 secured, in part, to a secondary crown 21 surrounding the cylindrical peripheral surface of the secondary mirror 20 and ensuring the attachment of the secondary mirror 20 to the frame 30. With reference to the FIG. 3 , the frame 30 comprises three arms 30.1, 30.2 and 30.3 which are arranged substantially in a triangle tangentially to the secondary crown 21 and which have their central part curved towards the secondary crown 21 and fixed thereto. The arms 30.1, 30.2 and 30.3 each have two ends and are fixed two by two by said ends forming a vertex 31 of the triangle. Consequently, the frame 30 comprises three vertices 31.1, 31.2, 31.3 each formed by the junction of two of the arms 30.1, 30.2 and 30.3 of the frame 30.

Each arm 30.1, 30.2, 30.3 has an inner surface facing the secondary crown 21 and an outer surface, opposite the inner surface.

The telescope 1 also comprises an articulated structure 40 and a plurality of piezoelectric actuators 50.

The piezoelectric actuators 50 are secured to the support 11 by any suitable means and for example by screwing, bolting, etc.

The articulated structure 40 comprises three pairs of legs 41, 42 and 43.

In reference to the FIG. 2 , the legs of pair 41 are referenced 41.1 and 41.2, the legs of pair 42 are referenced 42.1 and 42.2, and the legs of pair 43 are referenced 43.1 and 43.2.

Each of the legs extends in a longitudinal direction specific to it. Thus, leg 41.1 extends along an axis X _41.1 . Equivalently, leg 41.2 extends along an axis X _41.2 . Equivalently, leg 42.1 extends along an axis X _42.1 . Equivalently, leg 42.2 extends along an axis X _42.2 . Equivalently, leg 43.1 extends along an axis X _43.1 . Equivalently, leg 43.2 extends along an axis X _43.2 .

Furthermore, the pairs of legs 41, 42 and 43 have first ends spaced apart from each other and each connected to the support 11 via one of the piezoelectric actuators 50, and second ends close to each other and connected to one of the vertices 31.1, 31.2 and 31.3 of the frame 30.

In reference to the FIG. 4 , each of the legs 41.1, 41.2, 42.1, 42.2, 43.1 and 43.2 is connected by its first end to one of the piezoelectric actuators 50 via a spherical connection 61 (or ball joint connection). The spherical connection 61 allows rotation around three orthogonal axes allowing three degrees of freedom.

On the other hand, each of the legs 41.1, 41.2, 42.1, 42.2, 43.1 and 43.2 is connected by its second end to one of the vertices 31.1, 31.2 and 31.3 of the frame 30 by means of a double pivot connection 60. The double pivot connection 60 allows rotation around two orthogonal axes allowing two degrees of freedom.

In the extension of the legs 41.1, 41.2, 42.1, 42.2, 43.1 and 43.2, the piezoelectric actuators 50 are responsible for the actuation of a prismatic link 62. The prismatic link 62 allows a translation and makes it possible to achieve a degree of freedom.

As a result, each of the legs 41.1, 41.2, 42.1, 42.2, 43.1 and 43.2 of the articulated structure 40 comprises a double pivot link 60, a spherical link 61 and a prismatic link 62. All of these links allow six degrees of freedom of the secondary mirror 20 with respect to the primary mirror 10. The six degrees of freedom correspond to three translations in an orthonormal frame of reference (not shown) and three rotations (not shown). The three rotations correspond to heading, rolling or pitching.

With reference to figures 5, 6 and 7, the telescope 1 comprises at least one sensor 70 of a relative alignment of the primary mirror 10 and the secondary mirror 20. Preferably, the telescope 1 comprises at least two sensors 70 of the relative alignment of the primary mirror 10 and the secondary mirror 20. Preferably, the telescope 1 comprises three sensors 70.

Each sensor 70 is a non-contact position sensor.

Said sensor 70 is arranged to detect a position of a target secured to the secondary mirror 20. More precisely, said sensor 70 comprises a movable part and a fixed part. The movable part of the sensor 70 is adjacent to one of the vertices (31.1, 31.2 and 31.3) of the frame 30. The fixed part of the sensor 70 is, for its part, fixed to a frame 2 surmounting the support 11. This fixed part corresponds to the target secured to the secondary mirror 20.

The frame 2 surmounts the support 11. Preferably, the frame 2 is shaped into a cylinder.

Finally, the telescope 1 comprises an electronic processing unit (not shown), electrically connected to the piezoelectric actuators 50 and to the sensors 70 and arranged to control the piezoelectric actuators 50 as a function of the signals provided by the sensors 70 so as to maintain the alignment between the primary mirror 10 and the secondary mirror 20.

The operation of the present invention will now be described.

The position sensors 70 make it possible to measure the movements (translations and orientations) of the frame 30 and therefore of the secondary mirror 20 with respect to the primary mirror 10. When a movement is detected by one of the sensors 70, the signal provided by the sensors 70 contains corresponding information transmitted to the processing unit which controls the piezoelectric actuators 50 to maintain the alignment along the X axis of the secondary mirror 20 with respect to the primary mirror 10.

In reference to the FIG. 6 , the quantities measured by the different sensors 70 are as follows:

These quantities correspond to distances measured between the fixed part of the sensor 70 and the mobile part of the sensor 70. This measurement is preferably carried out at the level of the three vertices (31.1, 31.2 and 31.3) of the frame 30. Thus, each of the vertices is respectively named A, B and C to facilitate notation.

The relative position of the secondary mirror with respect to the primary mirror is thus determined by the following matrix:

For j = 1, 2 or 3, each element of the matrix l corresponds to a distance measured by the sensor 70.

Subsequently, we will denote the Laplace variable by s .

A first system describes the link between the forces generated by the six actuators, which we will denote F _i , and a position and orientation vector of the secondary mirror 20, which we will denote X.

The vector X is defined by six quantities including three positions (x, y and z) and three angles (Θ, Φ, and Ψ).

A matrix F brings together all the generated forces F _i .

The said first system can be described by a transfer matrix which will be noted G(s) and which is obtained by finite element modeling.

The corresponding real system is denoted G*.

The vector X is then defined as follows:

A second system describes the link between the said generated forces F _i and the nine lengths measured by the sensors 70. This system can be described by a transfer matrix, which we will denote by H(s), also obtained by finite element modeling.

The corresponding real system is denoted H*.

The vector is then defined as follows:

A gain matrix G(0) corresponds to the continuous gain of the system G(s).

Furthermore, N corresponds to the force factor of an actuator, mentioned in the manufacturer's specification sheet. In the case of the FIG. 8 , N=M(s=0) that is to say that the transfer function M(s) becomes a gain matrix N when s is zero.

In reference to the FIG. 8 , a control law makes it possible to guarantee that the alignment of the secondary mirror 20 with respect to the primary mirror 10 is maintained. The control law illustrated in FIG. 8 allows the position and orientation of the secondary mirror 20 to be controlled relative to the primary mirror 10, using the piezoelectric actuators 50.

• une matrice diagonale de correction K(s) 100 dans laquelle chaque composante diagonale est un correcteur K_i(s) permettant de stabiliser la boucle suivant le degré de liberté n°i ; chaque correcteur est choisi comme étant un correcteur proportionnel et le gain est choisi de manière à stabiliser la boucle totale ;
• une matrice de gains G(0)^-1101 issue de la modélisation d’éléments finis du système G(s), agencée pour linéariser et découpler le système jusqu’aux premiers modes mécaniques ;
• une matrice de gains 102 agencée pour convertir les efforts calculés en tension pilotable pour chacun des actionneurs 50 ;
• un actionneur réel M*(s) 103 ;
• un modèle réel du télescope T*(s) 104 défini comme suit ;
• une pluralité de capteurs C*(s) 105 et
• un estimateur f 106 agencé pour retrouver l’état X à partir des longueurs mesurées .

The control law includes:

• a diagonal correction matrix K(s) 100 in which each diagonal component is a corrector K _i (s) making it possible to stabilize the loop according to the degree of freedom n°i; each corrector is chosen as being a proportional corrector and the gain is chosen so as to stabilize the total loop;
• a gain matrix G(0) ^-1 101 resulting from the finite element modeling of the system G(s), arranged to linearize and decouple the system up to the first mechanical modes;
• a payoff matrix 102 arranged to convert the calculated forces into controllable voltage for each of the actuators 50;
• a real actuator M*(s) 103;
• a real model of the telescope T*(s) 104 defined as follows ;
• a plurality of sensors C*(s) 105 and
• an estimator f 106 arranged to find the state X from the measured lengths .

The estimator 106 can, for example, be obtained by the following relation:

Of course, the invention is not limited to the embodiment described but encompasses any variant falling within the scope of the invention as defined by the claims.

In particular, the telescope may have a structure different from that described above and for example a so-called “off-axis” telescope structure (see reflecting telescopes or reflection telescopes) in particular for applications linked to laser-based digital telecommunications.

All of the prismatic connections and all of the actuators are advantageously offset as close as possible to the support in order to reduce the mass on the pairs of legs. The prismatic connections and the actuators could nevertheless be arranged in the vicinity of the frame 30.

The contactless position sensor can be inductive, capacitive or eddy current. Their number can also be revised, six sensors for example allowing to find the six degrees of freedom describing the position and orientation of the secondary mirror 20 relative to the primary mirror 10.

Claims (10)

Telescope (1), comprising:

• a primary mirror (10) mounted on a support (11),
• a secondary mirror (20),
• an articulated structure (40) which is arranged between the support (11) and the secondary mirror (20) to allow six degrees of freedom of the secondary mirror (20) relative to the primary mirror (10),
• a plurality of piezoelectric actuators (50) mounted to move the secondary mirror (20) by acting on the articulated structure (40),
• at least one sensor (70) of an alignment of the primary mirror (10) and the secondary mirror (20),
• an electronic processing unit electrically connected to the actuators and arranged to control the actuators (50) so as to maintain the alignment between the primary mirror (10) and the secondary mirror (20).

Telescope (1) according to claim 1, comprising a secondary crown (21) mounted around the secondary mirror (20) and connected by a frame (30) to the articulated structure (40). Telescope (1) according to claim 2, in which the frame (30) comprises three arms (30.1, 30.2 and 30.3) which are arranged substantially in a triangle tangentially to the secondary crown (21) and which each have two ends, the arms are fixed two by two by their ends forming a vertex of the triangle (31), the vertices (31.1, 31.2 and 31.3) being fixed to the articulated structure (40). Telescope (1) according to claim 3, in which the articulated structure (40) comprises three pairs of legs (41, 42 and 43), the legs of each pair having first ends spaced apart from each other and each connected to the support (11) via one of the piezoelectric actuators (50), and second ends close to each other and connected to one of the vertices (31.1, 31.2 and 31.3) of the frame (30). Telescope (1) according to claim 4, wherein the first end of each of the legs is connected to the piezoelectric actuator (50) by a first spherical connection (61) and the second end is connected to the armature (30) by a second double pivot connection (60), the two connections being arranged to allow rotation of the armature (30) relative to the support (11). Telescope (1) according to any one of claims 4 and 5, wherein each of the piezoelectric actuators (50) is arranged to produce a translational movement in a longitudinal direction of the leg (41.1, 41.2, 42.1, 42.2, 43.1 and 43.2) to which it is connected. Telescope (1) according to any one of the preceding claims, in which the piezoelectric actuators (50) are attached to the support (11). Telescope (1) according to any one of the preceding claims, in which the sensor (70) is a non-contact sensor carried by a frame (2) surmounting the support (11) and arranged to detect a position of a target secured to the secondary mirror (20). Telescope (1) according to claim 8, wherein the non-contact sensor (70) is an inductive, or capacitive or eddy current position sensor. Telescope (1) according to any one of the preceding claims, in which the electronic unit controls the actuators (50) according to a control law arranged to maintain the alignment between the primary mirror (10) and the secondary mirror (20).