FR2696059A1 - Motor-couple with flat disc and angular movement control for e.g scanning mirror - has inductor of two magnetic armatures circumferentially and without contact to radial periphery with axial projections - Google Patents

Abstract

The motor-couple (8) has a rotatably movable inducer (31) in its interior and movable about the axis (X-X) and in contact with a stator (30) characterised in that the inducer has the form of a flat disc. The stator part is formed from at least one pair of magnetic armatures (32,33), circumferential but without contact to the external periphery of the disc. The stator part has two edges each (34,34A,35,35A) made of axial projections axial w.r.t. the disc, at least a portion looping around permanent coplanar magnets in each armature to generate a magnetic flux. The inducer has a flat coil (36) with an entry and an exit, formed of strands (36A) concentric around an arc of a circle and centred on the radial strand axis to form an ensemble of turns in the shape of a banana. The radial strands of each coil are grouped to form at least a pair of bundles of strands. Each of the bundles are axial to the respective armatures. Current is applied to the entry and exit of the coil and generates a magnetic flux. USE - Motor-couple to control movable shaft such as scanning mirror or antenna for use in space.

Description

 The invention relates to a torque motor without switching with an angular movement of less than 1800, as well as an application of this motor to control the angular movement of a shaft, for example carrying a scanning mirror (or even an antenna support, a filter, a lens, etc.), preferably but not exclusively in the space domain.

 Numerous varieties of torque motors are already known, that is to say motors whose operation is based on obtaining a torque, by virtue of the circulation of an electric current of appropriate intensity in wires. , in practice winding portions, placed in a permanent magnetic field. But known torque motors generally have a large size parallel to the axis of rotation, and / or a large inertia for the rotor (that is to say the rotating part of the motor) especially when it is the latter which carries the elements generating the permanent magnetic field (permanent magnets in practice).

 It is recalled here that the armature part of the motor which carries the wires traversed by the current is called the armature, and the complementary part of the motor carrying the elements generating the permanent magnetic field is called inductor.

 The subject of the invention is a torque motor without switching which combines a low rotational inertia, a small axial size (relative to the radial size), a large angular movement (although less than 1800), a constant torque (without ripple ) over almost all of the travel (for a given intensity), high precision, no diverging magnetic force (which allows easy combination with mounting on the rotor bearing), while being easy and simple to manufacture (d where low cost and high reliability).

 To this end, the invention provides a torque motor comprising an armature movable in rotation within a given angular movement around a given axis with respect to a stator part, characterized in that the armature has the overall in the form of a flat disc and in that the stator part carries an inductor formed from at least one pair of circumferentially disjoint magnetic armatures capping without contact the radially external periphery of this disc on disjoint angular sectors and each having two flanges forming axial projections axially opposite through the disc, at least one portion of crown with permanent magnetization coplanar with the axis being provided in each frame so as to generate a magnetic flux which is closed axially between the flanges through the armature, this armature comprising at least one planar winding, with an inlet and an outlet, formed of strands in a concentric arc and centered on the axis and radial strands connecting the strands in an arc so as to form at least one set of banana-shaped turns nested one inside the other but connected in series, the radial strands of each winding being grouped in at least a pair of bundles formed of adjacent but disjointed strands such that when a current is applied between the input and the output of the winding, all the radial strands of the same bundle are traversed by currents of the same radial direction, each of the bundles being disposed axially between the edges of a respective armature, the axial direction of the flow passing through the armature between the edges of each armature being chosen so that, when a current is applied between the input and the output of the winding, l interaction between the currents flowing in the strands of the beams with the axial magnetic flux generates couples of the same direction on the armature, the angular amplitude of the deflection being defined by the difference between the angular amplitudes of the pairs of flanges and the bundles of radial strands.

 According to preferred arrangements of the invention, possibly combined - said crown portion with permanent magnetization of each frame constitutes one of the edges of this frame, this crown portion being with permanent axial magnetization, - the two edges of each frame are consisting of crown portions with permanent axial magnetizations, in the same direction, - this motor comprises a single pair of diametrically opposed armatures, and a single pair of bundles per coil, diametrically opposed, - the angular amplitude of each armature is included between 900 and 1700, - the angular amplitude of each beam is less than approximately 300, - the angular amplitude of each armature is approximately 1500, the angular amplitude of each beam is approximately 300, and the amplitude of travel is around 1200, - the armature is formed by several windings mounted in series and arranged in axially superimposed layers but electrically nt isolated from each other, the input of each winding being however connected to the output of the previous winding, and the bundles of the windings whose strands are traversed at all times by currents of the same radial direction being superposed axially, - the armature is formed from 2 to 10 layers of windings, - the windings are formed by printed circuit tracks.

 The invention also relates to a device for controlling the angular movement of a rotating body, for example a scanning mirror possibly on board an observation satellite, comprising a torque motor having the above-mentioned properties, which is at low level vibration in service and without friction, which is precise, stable and reliable while advantageously allowing a slight tilting of the axis of rotation (typically of the order of a milliradian), all in a possibly spatial environment.

 To this end, the invention provides a device for controlling the angular movement of a mobile assembly, comprising a stator, a shaft linked to this mobile assembly and extending along a given axis and a motor of the aforementioned type for driving this movement in motion. shaft relative to the stator, this shaft being mounted in a magnetic bearing.

 According to other preferred arrangements of the invention, possibly combined - this magnetic bearing has two controlled transverse axes and comprises an annular ring with axial permanent magnetization taken between two polar annular parts and linked to the shaft and, radially on the side and on the other side of this ring, two pairs of coils surrounding axial cores caught between pole plates, and a magnetic flux closing ring, - this device comprises a tilting control device comprising a plurality of coils suitable for applying to the 'shaft a torque transverse to the axis of rotation, - the coils of this plurality of coils are arranged around cores arranged at least approximately axially opposite a rotor portion linked to the shaft, on either side both of this portion and of the axis of rotation of this shaft, - this device comprises a tilting control device comprising one of the pairs of bearing coils and a control unit adapted to offset the set radial position of the shaft transversely to the axis of rotation, - this device includes a locking device adapted to hold the shaft radially in a given configuration, - this locking device is arranged axially between the magnetic bearing and the motor, - this locking device comprises a plurality of clamps provided with clamping pads, articulated on a stator part around axial pins located at a distance from the axis, movable under the action of a maneuvering piece between an unlocking configuration in which the pads are at a maximum distance from the axis and a locking configuration in which these pads are at a minimum distance from the axis capable of inducing a radial tightening of the shaft, - the shaft has axial stops, for example formed by the edges of an annular groove, adapted to come opposite re axially frame the clamping pads in the locking configuration, for axial retention, - the operating part is an annular ring centered on the axis having a given angular clearance, comprising as many axial pins as there are of clamps, each clamp comprising a circumferential lumen traversed by one of the nipples, the radially internal and external edges of this lumen forming ramps for the nipples, this lumen comprising a first circumferential end situated at a minimum distance from the axis of rotation and a second circumferential end situated at a maximum distance from the axis of rotation, whereby, when the pins of the ring are in the first circumferential ends of the slots, the clamps are in their unlocking configurations and when the pins the ring are in the second circumferential ends of the lights, the clips are in their co locking configurations, - the pins are each provided with bearings adapted to roll on the radially internal or external edges of the circumferential openings, - the ring is controlled in angular movement by a second motor comprising a second armature integral with the ring and a second inductor linked to the stator part of the angular displacement control device, this second armature having the overall shape of a flat disc and the second inductor being formed of at least one pair of circumferentially disjointed magnetic frames covering the radially external periphery without contact of this disc on disjointed angular sectors and each having two flanges forming axial projections axially opposite through the disc, at least a portion of crown with permanent magnetization coplanar to the axis being provided in each frame so as to generate a flux magnetic closing axially between the flanges s through the second armature, this second armature comprising at least one planar winding, with an inlet and an outlet, formed of strands in a concentric arc and centered on the axis and of radial strands connecting the strands in a circular arc sort of forming at least one set of banana-shaped turns nested one inside the other but connected in series, the radial strands of each winding being grouped into at least one pair of bundles formed of adjacent but disjoint strands such that, when a current is applied between the input and the output of the winding, all the radial strands of the same bundle are traversed by currents of the same radial direction, each of the beams being disposed axially between the edges of a respective reinforcement, the direction axial flow through the second armature between the edges of each armature being chosen so that, when a current is applied between the input and the output of the winding, the interaction between the currents flowing in the strands of the beams with the axial magnetic flux generates on the second armature couples of the same direction, the angular amplitude of the deflection of the ring being defined by the difference between the angular amplitudes of the pairs of flanges and strand beams radial, - the shaft deflection control motor and the ring deflection control motor have common armatures with, between the armatures of the two motors and between the edges of the common armatures, isolated partially annular fixed magnetic parts magnetically with respect to the stator part, - the clamping pads are biased radially towards the axis by elastic elements acting on the ring, - the operating ring is connected to a stator portion by a plurality of elastic elements, generally radial, working in compression, movable in a plane transverse to the axis on either side of a configuration unstable tion in which they are oriented radially, between two extreme stable configurations for which clamps are in their locking or unlocking configurations, respectively.

 It will be appreciated that, according to one aspect of the original invention per se, advantage is taken of the games that constitute the radial air gaps of the magnetic bearing in which the shaft is mounted to allow this shaft to tilt, minimal, of course, but in practice sufficient, for example to compensate for the advance on its orbit of a satellite on which is embarked an angular displacement control device carrying a scanning mirror with an axis parallel to the orbit. This tilting is advantageously controlled by modifying the set position of the shaft in its magnetic bearing, which is for this purpose advantageously chosen so as to have at least one active radial axis (transverse to the axis around which it is sought to have a tilting) or even by axial actions of opposite directions applied in diametrically opposite zones of the rotor part of this bearing.

Objects, characteristics and advantages of the invention appear from the following description, given by way of nonlimiting example, with reference to the appended drawings in which
- Figure 1 is a schematic view in axial section of a control device in angular movement
- Figure 2 is an axial view, partially broken away, of the magnetic bearing of Figure 1
- Figure 3 is a principle view of this bearing in axial section along the line III-III of Figure 2
- Figure 4 is a principle view of the motor of Figure 1, in axial section along the lines IV-IV of Figures 5 and 6
- Figure 5 is a front view of the stator part of this motor, seen along the line VV of Figure 4 ;;
- Figure 6 is a sectional view of the movable wetness disc, along the section line VI-VI of Figure 4
- Figure 7 is a partial view in axial view of the angular resolver of Figure 1
- Figure 8 is an enlarged and complete view of the tilting control device of Figure 1
- Figure 9 is a principle view in axial section of a bearing and a tilting control device according to an alternative embodiment
- Figure 10 is a partial transverse view of the locking device, along line XX of Figure 1
- Figure 1i is another partial transverse view of this device, along the line XI-XI of Figure 1; and
- Figure 12 is a block diagram of the control electronics of the device of Figure 1.

 FIG. 1 represents, under the general reference 1, a device for controlling angular movement comprising a stator part 2, intended to be fixed to a support 3, for example a satellite in a terrestrial orbit, and a rotor part 4, rotatably mounted with respect to the stator part 2 around an axis XX, for example parallel to the aforesaid orbit, comprising a shaft 5 and a useful portion 6 such as a scanning mirror.

 This device 1 is mainly formed by a bearing 7, a motor 8, a possible angular resolver 9, a locking device 10 (advantageously disposed axially between the bearing and the motor, which improves the maintenance of the shaft), a tilting control device 11, and an electronic unit 12 controlling the operation of the various components of the device 1. The reference 13 designates radial position sensors used for the operation of the bearing 7.

 The bearing 7 is of the active magnetic type, so as to be free from any friction and from all the disadvantages usually associated with friction (vibrations, hysteresis phenomenon in the event of reversal of the direction of movement, etc.) and which would be detrimental to good angular precision. It is unique here, which contributes to facilitate tilting (the center of mass of the rotor part is then preferably substantially in the plane of this bearing).

 The tilting control device 11, according to an original aspect in itself, takes advantage of the axial or radial deflection which exists in a bearing between rotor and stator to induce a tilting either by radial displacement of the rotor part of the palm, or by axial actions of opposite directions in two diametrically opposite zones of this rotor part.

 The motor 8 has a limited angular movement which can approach here (without reaching it) the value of 1800, it has a very flat conformation which gives it a much smaller axial size than known motors, (which allows it to be easily installed. on a control shaft, even a very short one) combined with a low inertia in rotation around XX.

 Its servo control here involves the angular resolver 9 which is used to detect the angular position of the rotor part 4 relative to the stator part. This resolver is of any suitable known type, here preferably magnetic rather than optical, which corresponds to greater simplicity and slightly higher tolerances.

 The locking device 10 has this original in itself that it is a reversible mechanical system of the self-centered collet type, which overcomes the disadvantages of pyrotechnic solutions (in particular pollution, mono- blow, insufficiently controlled manufacturing reproducibility, insufficient security in the event of human presence) and allows complete tests on the ground with several locks and unlocks.

 The various aforementioned stages are detailed below.

Various numerical values will be given (to clarify the example considered here), corresponding to the following specifications, for an on-board optical scanning system on satellite - aiming accuracy: 0.25 * 10-3 mechanical rad - stability over 150 ms: 0.085 * 10-3 mechanical rad - maximum travel: 113.9250 - induced disturbing torque
per reaction: 6 * 102N.m - transition time between two
aiming positions offset by
1.650 mechanical: 66 ms - mechanical mass: <4 kg - tilting amplitude: 1.38 * 10-3 rad - supply voltage: 22-37 V - lifetime: 4 years (storage) + 5 years
(service)
First of all, the structure and operation of the magnetic bearing 7 are shown in FIGS. 2 and 3.

 The magnetic bearing 7 is of a conventional type, known per se from for example US-4,470,644 (WEISSER) and already used in various space applications (flywheels of SPOT and HELIOS satellites in particular) or terrestrial (industrial bearings for electric turbines for example).

 This bearing 7 is here of the type with two transverse controlled axes (we sometimes speak of a bearing with active radial control and with passive axial control). This solution is particularly advantageous for reasons of small axial size. In the absence of this constraint, it is possible to prefer a bearing with passive radial control and with active axial control, which has advantages from an electronic point of view.

 It is recalled here that a magnetic suspension system can never be completely passive because it can be demonstrated that there is always at least one degree of freedom according to which the suspended part (rotor) is in a state of unstable equilibrium ( that is to say that the suspension has a negative stiffness according to this degree of freedom), which requires the implementation for this degree of freedom of an active loop with actuators of the coil type.

 As will be mentioned below, the fact that the bearing 7 is in active radial control has the advantage of making it possible, by modifying the control instructions, to control the tilting of the axis X-X of the shaft.

 As shown in FIGS. 2 and 3, this bearing comprises, on the rotor part side, a ring 20 of permanent magnets with axial magnetization, axially sandwiched between two annular flat pole pieces 21 and 22 as well as, on the stator part side , an outer ring 23 for closing a magnetic circuit with a U-shaped axial section, and an inner ring 24, comprising two annular flat pole pieces 25 and 26 enclosing four cores 27 each surrounded by a coil 28 and angularly offset by 900. In the pole pieces 25 and 26 are advantageously provided with slots 29 dividing these pieces into sectors of 900 which are only connected near the ring of magnets 20; these slots prevent magnetic leakage from one coil to another. Each radial servo axis (there are two here) are associated with two diametrically opposite coils, electrically connected to each other to form a circuit independent of that of the other axis.

 This ring of magnets is coupled to the central shaft by a plurality of arms 14.

 In this type of bearing, the rotor is passively recalled if it is moved axially or if it tilts along an axis perpendicular to the axis X-X.

 It will be appreciated that the coils and the magnets mix their fluxes (see FIG. 3). The permanent magnets of the crown 20 produce a static main flux while the coils, when excited by a current of given direction, generate an additional flux which is used to modulate the permanent or static flux existing in the air gaps and therefore to increase on one side of the crown (in Figure 3, on the external side) and decrease on the other side (in Figure 3, on the internal side) the radial force applied to the suspended part and therefore apply a force to the latter radial in direction and amplitude suitable for bringing this suspended part back into its equilibrium position. Just reverse the current in the coils to generate an opposite force.

Of course the coils associated with the same axis are mounted and supplied so as to always apply both forces of the same direction. An advantage of this arrangement is to offer a force / current characteristic which is quasi-linear: this allows the use, in the electronic unit, of simple linear amplifiers.

 In addition to the absence of friction (increasing the service life) and of "friction noise" (improving the angular precision), this bearing with permanent magnets has the following advantages - very reduced dimensions, - almost zero permanent consumption in the absence vibration disturbance, - radial, axial and tilting stiffness largely sufficient for the intended application.

An example of dimensioning of the bearing 7 is as follows - average diameter of the bearing rotor: 100 mm - air gaps (outside and inside): 0.50 mm - inertia of rotation of the rotor and of
its attachment to the axis: 5.8 * 10-4 kg.m2 - mass of magnets: 50 g - stiffness: axial: 62 N / mm
radial: 225 N / mm
tilting: 140 Nm / rd - radial stop clearance (radius): 0.20 mm - actuating coil
number of turns: 300
wire diameter: 0.25mm
takeoff intensity under ig and for
0.2 mm initial offset: 1.1 A
minimum take-off voltage :: 16 V
It should be noted that during ground tests, if the assembly is arranged along a vertical axis, the radial control loop does not require more electrical power than in flight: the weight of the suspended assembly does not not affect the radial position of the rotor. However, the take-off voltage and current indicated above have been dimensioned so as to be able to operate the bearing on the ground whatever its position; however, only the vertical position with weight compensation by an axial device (counterweight on pulley) is representative of weightless operation.

 In a variant not shown, the bearing is of the type with two controlled axes, the magnets and coils of which are carried by the stator (hence a low rotor inertia), as shown in patent US Pat. No. 4,918,345 (VAILLANT DE GUELIS and al.).

 The control is performed on the basis of the information given by the sensors 13 for the radial position of the rotor (two sensors per slaved axis). The magnetic bearing 7 can use either speed sensors or displacement sensors (it is within the reach of the skilled person to adapt the electronic unit accordingly).

 The stability of the rotor in magnetic levitation is ensured by two identical control chains each driving an axis, represented jointly under the reference 7A in FIG. 12. Each chain has three functions - a stage for processing the input signal, - a correction stage, - an amplification stage.

 Only the generation functions of the 50 kHz carrier frequency of the position sensors are common.

 This electronics receives as input an image signal of the position of the rotor; this is processed via a corrector which provides the transfer function necessary for the stability of the servo. A power amplifier interfaces with the bearing.

 Radial takeoff of the rotor from a stop position is carried out automatically without the addition of an additional function. Only the presence of the control voltage allows the rotor to take off relative to its stop position.

 As shown in FIGS. 4 to 6, the motor 8 used to control the angular displacement of the rotor part 4 is a torque motor with travel limited to approximately 1200, comprising a stator or inductor part 30 comprising a pair of poles and a rotor part also called armature 31, consisting of a disc carrying one or more planar windings, preferably each produced using printed circuit technology.

 More precisely, as is apparent from FIGS. 4 and 5, the inductor 30 comprises a pair of disjoint magnetic frames 32 and 33, covering without contact the periphery of the armature over angular sectors less than 1800 (for example 1500) and having edges forming axial projections or axially opposite poles across the armature and defining with it radial air gaps.

These armatures each carry at least one portion of crown with permanent magnetization 34 or 35 respectively, generating a magnetic flux which is closed axially through the armature. These crown portions with permanent magnetization 34 or 35 advantageously run along air gaps situated on either side of the armature 31 and are therefore axial magnetization.

 In the example considered here, the respective magnetic fluxes of the two plates cross the armature in respectively different directions, and the crown portions 34 and 35 have opposite axial magnetization directions.

 To properly control the magnetic flux through the armature, the latter is advantageously interposed axially between two portions of crown with permanent magnetization 34 and 34A, or 35 and 35A, for each frame.

The winding (s) formed on the armature 31 are formed by strands in arcs of a circle 36A centered on the axis
XX and connected by radial sections or strands 36B here distributed in two diametrically opposite sectors or bundles S1 and S2, for example of angular amplitude of approximately 300. These arcs of circle 36A and these radial sections 36B are connected so as to form a winding 36 having an input terminal E and an output terminal S.

 Such a winding 36 is shown in FIG. 6, it being specified that, for the clarity of the drawing, the spacing between the neighboring sections 36B or the neighboring arcs 36A has been exaggerated, and therefore minimized their number. It will be noted that the arcs of a circle extend over nearly 1800 and that the radial strands within each of the two sectors S1 and S2 are, when a current is applied between the terminals E and S, traversed by intensities of the same meaning. The arcs of a circle define with the radial sections of turns shaped like a "banana" and fitted into one another so as to form at least one set of turns, here two sets of turns arranged on either side with a diameter connecting sectors S1 and S2.One of the radial sections (here the median section of sector S1) connects the two sets of turns (which thus constitute two half-coils).

 The winding can be formed of wires but, as indicated above, the winding 36 can be produced by depositing tracks, according to the technology of printed products.

 The armature may comprise several windings 36 arranged in layers of axially superposed printed circuit and electrically isolated from each other (there may be several windings on the same layer), the input of each winding being however connected to the output of the previous, so that these windings are in series, and the bundles S1 and S2 of the various coils being respectively superposed axially, so as to add and not subtract the torques generated by the neighboring beams.

 The directions of current flow in the sectors are chosen so that, when each of the sectors is sandwiched (without contact to spare the aforementioned axial air gaps) in a respective armature, the permanent magnetization fluxes of the two armatures which close through sectors induce on the armature couples of the same direction.

 The strands in an arc are preferably located radially away from the flanges or pole portions so as to avoid as much as possible the generation of radial couples. On the other hand, the reinforcements are preferably deep enough to allow the aforementioned condition while preserving the radially outer strands from possible leakage fields.

 It will be appreciated that the current flowing in the circular arcs does not induce any torque on the armature.

 It will be appreciated that such a principle is generalized to motors with one phase and with n pairs of poles, as long as the desired clearance is less than 2ranz in which case provision is made on the armature for n pairs of diametrically opposite sectors; there may be one or more windings per layer of printed circuit, with banana turns extending from a sector corresponding to a pair of poles to an adjacent sector extending to another pair of poles.

As before, the amplitude of movement is defined by the difference of the angular amplitudes of the reinforcements and of the sectors or bundles of radial strands.

 It will be noted in this connection that the amplitude of the reinforcements is in fact the amplitude of the edges thereof and that it is only in a preferred manner that the bottom of the reinforcements has the same amplitude as these edges: in a variant this background radial could be of lower amplitude.

 Such a configuration makes it possible to obtain large torques with armatures of low mass therefore of low inertia of rotation; moreover, it has the advantage of providing a constant torque (therefore without ripple) for a given intensity over its entire angular displacement, that is to say here 1200 (the amplitude of each armature = 1500 - amplitude of each sector = 300) which does not could be obtained reliably with a synchronous motor or a motor switching between several pairs of poles. Another fundamental advantage of this motor 8 is the absence of divergent magnetic force (negative stiffness), which allows its use coupled with a magnetic bearing without additional stability problem to be resolved.

 This motor is powered by wires directly welded to the armature's input and output terminals, which is possible due to the limited travel of this armature.

For example, the main characteristics of this motor are - average diameter of the rotor / armature winding: 90 mm - max diameter of the rotor: 120 mm - induction in the air gap 0.3 to 0.4 T - number of layers rotor circuit 4 to 6 - rotor thickness 1.6 mm - rotor inertia 1.3 * 10-5 kg.m2 - maximum torque 6.10-2 Nm - intensity for max. 2A
Two technologies (known per se) for angular position detection are possible to obtain the required angular precision - optical resolver (case not shown): composed of an etched glass disc, and several pairs of emitters (optical diode) - receiver shifted by a quarter of engraving step to know the direction of rotation and improve the accuracy of the resolver. The disadvantage of this type of resolver is the very small clearance required between the disc on the one hand, and the transceivers on the other hand (a few tens of microns), which could prove to be incompatible with the flexibility of the associated magnetic bearing (or at least the axial backlash). On the other hand the electronics could be quite simple. This type of decoder would work in relative (incrementation - decrementation) and would require a reference for the zero position - magnetic resolver 9 with variable reluctance (case represented in figure 7) composed of a part rotating linked to the shaft (here via the rotor part 20 of the bearing 7) and advantageously formed of two toothed rings 40 and 41 offset both axially and radially (by half the angular distance between the teeth 40A or 41A of the crowns - there are for example 32 so that the radial offset is 5.6250 - to know the direction of rotation) and of a fixed part also composed of two toothed crowns 42 and 43 but whose teeth 42A and 43A are surrounded by coils 44 and 45.

 In the latter case, a sinusoidal alternating voltage is injected into the coils of each crown of the fixed part (all the coils are in series) and the output current traces the reluctance of the magnetic circuit thus formed: weak reluctance for the teeth opposite each other, and strong when the teeth of one crown are opposite the hollows of the other crown. The shape of the teeth is studied to have a sinusoidal output signal for a polar step: appropriate processing electronics (synchrodigital resolver designated by the reference 9A in FIG. 12) then makes it possible to know precisely the angular position on a polar step. This resolver is therefore mixed in operation: absolute on each pole step, relative (incremental) from one pole step to another. With 32 teeth on each crown and the synchrodigital resolver 9A, the desired precision is obtained. The advantage of this principle lies in the possibility of having relatively large air gaps (0.25 - 0.3 mm) compatible with the flexibility of the magnetic bearing.

 The input stages of the resolver 9A are analog and demodulate a polar step. The first stage of the electronics achieves from a voltage measurement, image of the sinusoidal variation of the inductor, a conversion by subtraction of a voltage of the same frequency, suitably calibrated in phase and in amplitude.

 The second stage is a synchrodigital converter in order to obtain a binary word proportional to the instantaneous angular position.

 The positioning of the mirror 6 at the requested setpoint value is achieved by a servo block shown diagrammatically at 8A in FIG. 12, the inputs of which are the information of the angular resolver and the sweep setpoint, the output being a control signal a .

 The actual control of the scanning motor (see block 8B of FIG. 12) is done using a linearity and crossover distortion current amplifier compatible with the required performance. This receives the analog command a as input and delivers a current of sign and amplitude proportional to the torque necessary for the servo of the scanning motor.

 Its supply takes place if possible directly from the unregulated voltage of a converter 15 connected to a supply bus by a filter and protection element 16.

 FIG. 8 shows in more detail and more completely the tilting control device 11.

 The latter comprises small coils 50 arranged around cores 51 arranged at least approximately axially opposite the rotor part, for example facing the crown 20 with permanent axial magnetization. These coils are arranged on either side axially of this rotor part in zones diametrically opposite the axis around which it is desired to be able to cause a tilting (this axis is perpendicular to the plane of FIG. 1). Only the coils 50 on the right are shown in FIG. 1 for reasons of readability.

 The tilting control is done by activating two coils 50 arranged on either side of both this rotor part and the axis thereof, so as to attract this rotor, in a zone in one direction axial and in a diametrically opposite zone in the opposite axial direction, which causes a transverse torque on the shaft. We take advantage here that the magnetic bearing has a positive stiffness in tilting.

 This torque is controlled by servo electronics, shown diagrammatically in 11A in FIG. 12, controlled on the one hand by the tilting instruction ss and, on the other hand, by the response of the sensors used to read the angle ss. These sensors may either be specific sensors (two position sensors mounted in differential located very close to the control coils, reading the position of the rotor), - be constituted by the two position sensor 13 of the magnetic bearing located in the perpendicular plane at the tilting axis, plus two sensors identical to those of the magnetic bearing, mounted in the same plane but offset axially.

 The advantages of this solution being on the one hand to use the same sensors for different functions.

 Another possibility for obtaining a tilting of the axis consists in conforming the pole pieces of the rotor and stator parts according to a very flattened cone which is very exaggerated in FIG. 9. Thus the simple control of the radial position of the suspended part corresponds to an inclination of the bearing axis. This solution eliminates all of the coils and sensors described above; but of course assumes that the electronics 11A for controlling the magnetic bearing is modified accordingly.

 This solution has the advantage of a slight reduction in weight (2 coils, 2 sensors and a part of electronics removed).

 In fact the aforementioned solutions aim to tilt the rotor part around an axis substantially included in the bearing plane.

 Assuming that the rotor part is held radially in any location of the shaft 5 (for example by another magnetic bearing preferably identical to the bearing 7), a tilting can be obtained by simple modification of the radial equilibrium setpoint of the bearing, without structural modification thereof.

 The locking device 10 is shown in FIGS. 10 and 11.

 This device 11 comprises three clamps 60 each provided with a clamping pad 61 adapted, with the pads 61 of the other clamps, to grip the shaft 5. Preferably, as can be seen from FIG. 1, the pads fit into a circumferential groove in the shaft, the flanks of which, whether continuous or not, thus allow the shaft to be held axially, in at least one direction (more generally it may be sufficient for a few axial bearings for the edges of the pads).

 These clamps 60 are, in zones 62 offset both radially and circumferentially with respect to the pads 61, articulated on the stator part of the entire device, using axial pins 63.

 These clamps 60 are housed in a transverse slot of a ring 65 (see also FIG. 1) adapted to rotate around the axis X-X with a limited clearance, for example 600.

 Each of the clamps has a slot 66, the radially inner 67 and outer 67 ′ edges of which are not centered on the axis X-X, form ramps for an axial stud 68 integral with the ring and passing through this slot.

Preferably, these pins 68 are provided with bearing 68A which minimizes friction on the ramps. Each lumen 66 has a first circumferential end 69 close to the articulation 63 where the edge 67 is at a minimum distance from the axis of its shoe 61 and a second circumferential end 70 distant from the articulation 63, where the edge is at a distance maximum of the skate axis.

 The three axial pins 68 are positioned in the ring 65 through its slot so as to be simultaneously, either at the first circumferential ends 69 (unlocking configuration), or at the second circumferential ends 70 (locking configuration).

 This ring 65 is returned in rotation in a passive bistable manner by means of elastic elements 75 (based on springs) - see below - towards one or the other of the locking or unlocking configurations, thus guaranteeing on the one hand, in the unlocking configuration, the maintenance in this configuration and, on the other hand, in the locking configuration, not only the maintenance in configuration, but also the force applied by the pads on the shaft: in practice the lights 66 are dimensioned so that the clamping pads come to bear on the shaft before the pins come into circumferential abutment against the second circumferential ends 70.

 The ring 65 is maneuvered between its two configurations against the aforementioned passive bistable return elements, by a motor 71 which is advantageously of the same type as the motor 8; this motor 71 even includes here the same armatures (see FIG. 1) as the motor 8, with fixed magnetic parts 72 partially annular disposed between the armatures of the two motors and between the magnetized crown portions of the armature of FIG. 5 (the parts 72 having the same angular amplitude as these portions of crowns). This annular part 72 is fixed to the stator part by any suitable known non-magnetic means to avoid the appearance of magnetic leaks.

 Although the useful angular movement of the motor 71 is smaller than that of the motor 8, its armature can be, for the sake of simplicity, chosen with the same geometry as in FIG. 6.

 This motor is controlled by electronics shown diagrammatically at 10A in FIG. 12.

 It will be recalled here that the configuration of the motor 71, like that of the motor 8, allows a small axial size (especially if common frames are used), and a high torque.

 The ring 65, to which the armature of the motor 71 is fixed, is preferably connected to the magnetic annular part 72 (or to any stator part) by a plurality of elastic elements 75 (for example four or six) which are generally radial and working in compression, here articulated, movable transversely to the axis between two extreme configurations in which the clamps are in configuration, either locking, or unlocking; these elastic elements have an intermediate configuration (unstable equilibrium) in which they are oriented radially, whereby this locking device is made passively bistable. It will be appreciated (see above) that these elements thus have a double function since they generate the clamping force and ensure the bis table positioning.

 The elastic elements thus ensure - secure locking (not unlocking under vibration), - safe unlocking too, - reversibility of the locking / unlocking function.

 This solution makes it possible both to avoid the need for pyrotechnic release, to authorize during tests on the ground of the complete system several locks and unlocks and therefore to test the locking system itself. This system is therefore designed to operate several times on the ground, but a priori only once in flight for unlocking.

 From the power point of view (see Figure 12) the only source of energy required is the primary voltage of the power bus. At the input, the power supply electronics includes (block 16 already mentioned) the necessary protections in order to preserve the integrity of the power supply as well as the useful filtering.

 Subsequently, one or more converters 15 provide the voltages necessary for all the electronics of the scanning system, it performs the galvanic isolation.

 The reference 17 in FIG. 12 represents the interface and protection block of the assembly with respect to the on-board computer (and vice versa) to which it is connected by a control bus and a monitoring bus.

 It is possible to provide, if necessary, a dynamic compensation system aimed at eliminating, or at least greatly reducing the reaction torque transmitted to the satellite. The principle of this system would reside in the rotation of a flywheel in the opposite direction to that of the mirror. Various solutions are possible but the only one which appears feasible in a reliable manner (although penalizing from the mass point of view) without degrading the level of angular precision on the scanning consists in installing in the axis of the main system another magnetic bearing, results in rotation by a motor strictly identical to that of the sweeping system and coupled to a flywheel. No mechanical connection (gears) then connects the main system to this new bearing-motor-flywheel assembly; simply the two motors (sweeping and dynamic compensation) are connected together (in series to have the same torque) in opposition: the sweeping control thus activates both the system carrying the mirror and the flywheel. The resulting torque transmitted to the satellite is therefore of the level of the difference in torque between the two motors, or of the level of the difference between the inductions of the stator magnets of each of the two motors.

 It goes without saying that the above description has been offered only by way of nonlimiting example and that numerous variants can be proposed by those skilled in the art without departing from the scope of the invention. Thus, for example, the resolver can be eliminated, for example when the motor rotor is subjected to an elastic return towards a given configuration with respect to the stator.

Claims (24)

 1. Torque motor (8) comprising an armature (31) movable in rotation within a given angular movement around a given axis (XX) relative to a stator part (30), characterized in that the armature (31) generally has the shape of a flat disc and in that the stator part (30) carries an inductor formed of at least one pair of circumferentially disjoint magnetic frames (32, 33) capping without contact the radially external periphery of this disc on disjointed angular sectors and each having two flanges (34, 34A, 35, 35A, 72) forming axial projections axially opposite through the disc, at least one portion of crown (34, 34A, 35, 35A) with permanent magnetization coplanar to the axis being provided in each frame so as to generate a magnetic flux which is closed axially between the flanges through the armature, this armature comprising at least one planar winding (36), with an inlet and an outlet, formed of strands in an arc (36A) concentric and centered on the axis and radial strands (36B) connecting the strands in a circular arc so as to form at least one set of banana-shaped turns nested one inside the other but connected in series, the radial strands (36B) of each winding being grouped into at least one pair of bundles formed of adjacent but disjoint strands such that when a current is applied between the input and the output of the winding, all the radial strands of the same beam are traversed by currents of the same radial direction, each of the beams being disposed axially between the edges of a respective armature, the axial direction of the flow passing through the armature between the edges of each armature being chosen so that when a current is applied between the input and the output of the winding the interaction between the currents flowing in the strands of the beams with the axial magnetic flux generates on the armature couples of same direction, the angular amplitude of the deflection being defined by the difference between the angular amplitudes of the pairs of flanges and the bundles of radial strands.  2. Torque motor according to claim 1, characterized in that said portion of the crown with permanent magnetization of each frame constitutes one of the edges of this frame, this portion of crown being with axial permanent magnetization.  3. Torque motor according to claim 2, characterized in that the two flanges of each frame consist of crown portions (34, 34A, 35, 35A) with permanent axial magnetizations in the same direction.  4. Torque motor according to any one of claims 1 to 3, characterized in that this motor comprises a single pair of diametrically opposed reinforcements, and a single pair of bundles per coil, diametrically opposite.  5. Torque motor according to claim 4, characterized in that the angular amplitude of each frame is between 900 and 1700.  6. Torque motor according to claim 4 or claim 5, characterized in that the angular amplitude of each beam is less than approximately 300.  7. Torque motor according to claim 4, characterized in that the angular amplitude of each armature is approximately 1500, the angular amplitude of each beam is approximately 300, and the amplitude of movement is approximately 1200 .  8. Torque motor according to any one of claims 1 to 7, characterized in that the armature is formed by several windings mounted in series and formed in axially superimposed layers but electrically isolated from each other, the input of each winding being however connected to the output of the previous winding, and the bundles of the windings whose strands are traversed at all times by currents of the same radial direction being superimposed axially.  9. Torque motor according to claim 8, characterized in that the armature is formed from 2 to 10 layers of windings.  10. Torque motor according to any one of claims 1 to 9, characterized in that the windings are formed by printed circuit tracks.  11. Device for controlling the angular movement of a mobile assembly (4), comprising a stator, a shaft (5) linked to this equipment and extending along a given axis (XX) and a motor (8) according to the any one of claims 1 to 10 for driving this shaft in movement relative to the stator, this shaft being mounted in a magnetic bearing (7).  12. Control device according to claim 11, characterized in that this magnetic bearing is with two transverse controlled axes and comprises an annular ring (20) with permanent axial magnetization taken between two annular pole pieces (21, 22) and linked to the shaft and, radially on either side of this ring, two pairs of coils (28) surrounding axial cores (27) caught between pole plates (25, 26), and a ring (23) for closing the flow magnetic.  1 3. Control device according to claim 11 or claim 12, characterized in that this device comprises a tilting control device comprising a plurality of coils (50, 28) adapted to apply to the shaft a transverse axis torque rotation (xx).  14. Control device according to claim 13, characterized in that the coils (50) of this plurality of coils are arranged around cores (51) arranged at least approximately axially opposite a rotor portion connected to the shaft, on both sides of both this portion and the axis of rotation of this shaft.  15. Control device according to claim 12, characterized in that it comprises a tilting control device comprising one of the pairs of bearing coils and a control block (11A) adapted to offset the radial position of the setpoint. the shaft transversely to the axis of rotation (XX).  16. Control device according to any one of claims 11 to 15, characterized in that it comprises a locking device (10) adapted to hold the shaft radially in a given configuration.  17. Control device according to claim 16, characterized in that this locking device (10) is arranged axially between the magnetic bearing and the motor.  18. Control device according to claim 16 or claim 17, characterized in that this locking device comprises a plurality of clamps (60) provided with clamping pads (61), articulated on a stator part around axial pins (63 ) located at a distance from the axis, movable under the action of an operating part (65) between an unlocking configuration in which the pads are at a maximum distance from the axis and a locking configuration in which these pads are at a minimum distance from the axis suitable for inducing radial tightening of the shaft.  19. Control device according to claim 18, characterized in that the shaft has axial stops adapted to come axially opposite the clamping pads in the locking configuration, whereby this shaft is held axially in said locking configuration .  20. Control device according to claim 18 or claim 19, characterized in that the operating part (65) is an annular ring centered on the axis having a given angular movement, comprising as many axial pins (68) as there are clips, each clip comprising a circumferential lumen (67) through which one of the studs (68) passes, the radially internal and external edges (69, 70) of this lumen forming ramps for the studs, this lumen comprising a first circumferential end (69) located at a minimum distance from the axis of rotation and a second circumferential end (70) located at a maximum distance from the axis of rotation, whereby, when the pins of the ring are in the first circumferential ends of the lights, the pliers are in their unlocking configurations and when the pins of the ring are in the second circumferential ends of the lights es, the clamps are in their locking configurations.  21. Control device according to claim 20, characterized in that these axial pins are each provided with bearings (68A) adapted to roll on the radially internal or external edges of the circumferential slots.  22. Control device according to claim 20 or claim 21, characterized in that the ring is controlled in angular movement by a second motor (71) comprising a second armature integral with the ring and a second inductor linked to the stator part ( 2) of the angular displacement control device, this second armature having the overall shape of a flat disc and the second inductor being formed of at least one pair of circumferentially disjoint magnetic armatures capping without contact the radially external periphery of this disc on disjointed angular sectors and each having two flanges forming axial projections axially opposite through the disc, at least a portion of crown with permanent magnetization coplanar to the axis being provided in each frame so as to generate a magnetic flux which closes axially between the flanges through the second armature, this second armature comprising at least one flat winding, with an input and an output, formed of strands in a concentric arc and centered on the axis and of radial strands connecting the strands in a circular arc so as to form at least one set of nested banana-shaped turns one inside the other but connected in series, the radial strands of each winding being grouped into at least one pair of bundles formed of adjacent but disjoint strands such that, when a current is applied between the input and the output of the winding, all the radial strands of the same beam are traversed by currents of the same radial direction, each of the beams being disposed axially between the edges of a respective armature, the axial direction of the flow passing through the second armature between the edges of each armature chosen so that, when a current is applied between the input and the output of the winding, the interaction between the currents flowing in the strands of the beams with the magnet fluxes ics axial generates on the second armature couples of the same direction, the angular amplitude of the clearance and the ring being defined by the difference between the angular amplitudes of the pairs of flanges and the bundles of radial strands.  23. Control device according to claim 22, characterized in that the motor (8) for controlling the movement of the shaft and the motor (71) for controlling the movement of the ring have common frames with, between the armatures of the two motors and between the edges of the common frames, partially annular fixed magnetic parts (72) magnetically isolated from the stator part (2).  24. Control device according to any one of claims 20 to 23, characterized in that the clamping pads are biased radially towards the axis by elastic elements (75) acting on the ring (65).  25. Control device according to any one of claims 20 to 24, characterized in that the operating ring is connected to a stator portion by a plurality of elastic elements (75) generally radial, working in compression, movable in a plane transverse to the axis on either side of an unstable configuration in which they are oriented radially, between two extreme stable configurations for which the clamps are in their locking or unlocking configurations, respectively.