Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
  • G01C21/00—Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00
  • G01C21/10—Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00 by using measurements of speed or acceleration
  • G01C21/12—Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00 by using measurements of speed or acceleration executed aboard the object being navigated; Dead reckoning
  • G01C21/16—Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00 by using measurements of speed or acceleration executed aboard the object being navigated; Dead reckoning by integrating acceleration or speed, i.e. inertial navigation
  • G01C21/165—Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00 by using measurements of speed or acceleration executed aboard the object being navigated; Dead reckoning by integrating acceleration or speed, i.e. inertial navigation combined with non-inertial navigation instruments
  • G01C21/1654—Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00 by using measurements of speed or acceleration executed aboard the object being navigated; Dead reckoning by integrating acceleration or speed, i.e. inertial navigation combined with non-inertial navigation instruments with electromagnetic compass
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F41—WEAPONS
  • F41G—WEAPON SIGHTS; AIMING
  • F41G3/00—Aiming or laying means
  • F41G3/22—Aiming or laying means for vehicle-borne armament, e.g. on aircraft
  • F41G3/225—Helmet sighting systems

Definitions

• Hybrid magnetic inertial system determining position and orientation of a moving body
• the field of the invention is the measurement of the position and the orientation of a moving body M, which moves in translation and in rotation with respect to a reference frame linked to a fixed or movable structure P with respect to a fixed reference reference type reference Galilean.
• the invention concerns the determination of the position and the orientation (P / 0) of a pilot's helmet in the reference reference of the aircraft, P / O from which the angular position of a target outside is determined in this same reference by the aim through a system comprising the helmet visual pilot.
• the pilot superimposes on the external target the image of a collimated cross projected on its transparent visor, and acquires the measurement made by the device by pressing a push button.
• the main problem of determining the position and orientation of a moving body with respect to a reference reference linked to a fixed or mobile structure to be determined with precision comes from an electromagnetic environment highly disturbed by radiated magnetic fields (EMI for Electromagnetic Interferences, ECI for Eddy Currents Interferences or fields due to eddy currents) and / or magnetic fields induced by ferromagnetic bodies (IMF for FerroMagnetic Interferences), environments such as the cockpits of aircraft and more particularly helicopters, surgical operating theaters, etc.
• EMI Electromagnetic Interferences
• ECI Electromagnetic Interferences
• IMF FerroMagnetic Interferences
• US Pat. No. US 7,640,106 describes an apparatus for determining the position of a selected object with respect to a moving reference image, the apparatus comprising at least one integral transmission-reception frame assembly reference. of the reference frame moving, at least one transceiver assembly object securely fixed to the selected object, an inertial measurement the unit firmly fixed to the selected object, an inertial navigation system integral with the reference image mobile, and a tracking processor coupled with the object assembly of the transceiver, the inertial measurement unit and the inertial navigation system, the object assembly of the transceiver communicating with the frame assembly.
• the inertial measurement unit produce IMU inertial measurements of the movement of the selected object relative to a fixed inertial reference frame
• the inertial navigation system produces INS inertial measurements of moving the reference frame moving relative to the fixed inertial reference frame
• the tracking processor receive electromagnetic measurements resulting from the magnetic communication between The reference frame transmitter-receiver assembly and the object assembly of the transceiver, the tracking processor of determining the position of the selected object relative to the moving reference image using IMU inertial measurements and INS inertial measurements to optimize electromagnetic measurements.
• a second set of orthogonal magnetic field receiving coils integral with the object, and forming a sensor, each of the coils belonging to a path of the sensor.
• Such a device comprises means:
• US patent US5646525 describes another example of equipment for determining the position and orientation of a helmet worn by a crew member of a vehicle comprising a generator, associated with the vehicle, which produces a magnetic and electric field fixed force rotator, orientation and frequency in at least a portion of the vehicle.
• the apparatus also comprises a plurality of detectors each of which generates a signal proportional to at least one of the electric or magnetic fields at least one point associated with the helmet and calculating the circuits responsive to the signal for determining the coordinates of the at least one a point relative to the generator and intended to determine the position and orientation of the helmet.
• US Patent US6400139 also discloses an exemplary position tracking / orientation apparatus in a limited volume.
• control detector having a fixed position and orientation near or within the volume to represent electromagnetic distortion.
• the probe detectors are placed on an object to be pursued within the volume and the output of each detector detector is used to calculate the parameters of a non effective real electromagnetic source.
• the parameters of the effective source serve as inputs for the calculation of the position and orientation measured by each detector-probe, as if the object were in the electromagnetic field without distortion produced by the source or the efficient sources.
• the invention is useful for any electromagnetic tracking system that may be subject to distortion or electromagnetic interference.
• US7640106 requires a first inertial sensor in the helmet and a second inertial sensor and an estimator (Kalman filter) to determine an orientation of an object.
• This solution requires the provision of a sensor on the fixed platform. It aims to know the angular orientation of the helmet in the benchmark of the platform. This angular orientation is determined by the integration of the estimated relative velocity. This relative speed is obtained by differentiating between: the angular velocity of the moving body measured at the output of an angular velocity sensor IMU fixed in the moving body whose orientation is to be determined, measured in a fixed inertial reference mark (Galilean reference) and
• this solution does not take into account the strong electromagnetic disturbances observed in a real cell, for example a helicopter or airplane cell.
• the object of the invention relates to a system as set forth in claim 1, designed to overcome the drawbacks of the prior art and to establish a method and perform a method of eliminating electromagnetic disturbances (ECI: currents of Foucault, IMF: induced ferromagnetism) in real time without requiring the very expensive need to map the useful volume swept by the sensor.
• ECI electromagnetic disturbances
• IMF induced ferromagnetism
• Another object of the invention is to improve the signal / noise ratio S / B of the P / O detector to obtain the required performances in environments highly disturbed by the EMI (for example in aircraft and more specifically in helicopters: radiated fields created by the on-board generators, on-board equipment).
• the S / N signal to noise ratio can be expressed as the ratio between the standard deviation of the signal Se that the sensor would receive in "free space” that is to say without any electromagnetic disturbance and the standard deviation of the noise.
• B the noise being the sum of all the signals not coming directly from the transmitter (inductive field).
• the objective of the invention is to achieve an improvement in the S / N ratio of the order of 1000 for the most critical cases (helicopters).
• a third object of the invention is to compensate for the latency of the output information by hybridization with an inertial system.
• the method consists in optimizing the winding shapes of the emission axes in order to increase the number of turns for a given wire diameter and to introduce a core of very permeable material of particular shape making it possible to increase the induction emitted in reports. greater than 10: El.
• E-2 servocontrol of the magnetic field system using E-3 sensors (also called “E-sensors”) included in the coils of the transmission axes.
• the noisy signal is measured by the reception set C-1, the noise Sp is measured and estimated from the measuring device C-2. It will be described later that in a particular embodiment, depending on the environmental conditions, the noise can be estimated from the device C-1 preferably in a time during which no current is sent in the coils El by E- 4.
• This filtering is carried out in the processor 4-4 by constructing a temporal model of the preceding disturbances and estimating the parameters by an optimal or sub-optimal filter in real time over short times. T off during which the currents injected into El are zero. Variables in this model are time-varying, independent, or statistically weakly correlated variables that represent variations in useful signals and noises.
• an embodiment S b of the ambient noise is measured by a sensor block C2, of which is modeled as before a complete model. The parameters of this model are used to remove by subtraction all the components of S b correlated with the fields emitted by El.
• the uncorrelated noise is extracted to become a variable independent of the linear magnetic model of the signals measured by the C-1 sensor. fixed on M.
• the parameters of the only model of the fields emitted by the axes of the transmitter (said field of "free space” undisturbed) and in particular the matrix allowing to calculate in a known manner the position and orientation of the moving object.
• the currents injected into the windings which create the inductions are preferably simultaneous.
• the measured inductions are therefore the sum of the fields emitted at time t and the fields present in the environment.
• the invention therefore aims to distinguish in the measured field each component emitted by each transmission axis.
• This recognition of the field emitted by one of the components constitutes a demultiplexing of the inductions that can be described as functional, as opposed to the inventions cited which make either a temporal demultiplexing (non-simultaneous transmission but sequenced in time) or frequency demultiplexing (frequency detection in the spectral domain).
• a temporal demultiplexing non-simultaneous transmission but sequenced in time
• frequency demultiplexing frequency detection in the spectral domain
• the principle of the invention consists in using the attitude provided by the magnetic position detection means expressed in the fixed inertial frame to reset or initialize the calculation of the attitude of the IMU gyrometric sensors obtained. by integration in the reference frame of a dynamic equation of prediction of a quaternion.
• the attitude of the position detecting means expressed in the inertial mark simply uses the attitude of the platform provided by the INS, in the form of three Euler or DCM matrix angles (matrix of the director cosines of the platform) or quaternion calculated from the Euler angles or the DCM matrix.
• the dynamic model of prediction computed at a high rate, is recaled at the time t- L , T L being the latency time of the magnetic position detection means, at each arrival of the quaternion provided by the magnetic position detection means.
• T L being the latency time of the magnetic position detection means, at each arrival of the quaternion provided by the magnetic position detection means.
• the invention also includes the real-time correction of the triaxial angular velocity sensor by estimating the errors of the sensor.
• FIG. 1 represents a schematic view of a solution of the prior art
• FIG. 2 represents a schematic view of the reference object and benchmarks
• FIG. 3 and 3 ' is a schematic view of the architecture of the invention
• FIG. 4 represents a schematic view of the detailed architecture of the invention
• FIG. 5 represents a schematic view of the enslavement of the inductions issued
• FIG. 6 represents a schematic view of a transmitter block of the state of the art
• FIG. 7 represents the schematic view of the formation of an axis El of the transmitter according to the invention
• FIG. 8 represents exemplary embodiments of transmission axes
• FIG. 9 represents a schematic view of a core generator according to the invention
• FIG. 10 represents a schematic view of field servocontrol
• FIG. 11 represents the emission time diagram
• FIG. 12 represents a schematic view of the magnetic-inertial hybridization and the inertial extrapolator
• This device is disposed in a disturbed electromagnetic environment.
• An emitter E composed of Ne coils forming a quasi-orthogonal reference mark R E is fixed rigidly to the platform P.
• the matrix of passage R E / P between the emitter mark R E and the platform mark R p is assumed to be constant and measured during the laying of the mechanical reference of the transmitter in the platform P.
• the mark R p When the mark R p is movable relative to Ri, as is the case when the platform is an aircraft, the mark R p is defined in the reference Ri by the angles of Euler defining the attitude and calculated by the inertial unit or equivalent device and transmitted to the process of the invention.
• the quaternion Q PI as the matrix of passage R p / I between R p and R ⁇ represent the attitude of P with respect to R L.
• This last sensor is for example MEMS (Micro-Electro-Mechanical Systems) type.
• the Cl sensor is a magnetic fluxgate, fluxmeter, servo flowmeter, Hall effect sensor, AMR, GMR, TMR . Its axes are defined by the fixed transition matrix R c / M and identified in the factory in a known manner.
• a particular embodiment consists in adding a certain number of so-called sensor_B sensors represented by the block C-2 of FIG. 3. These sensors are fixed in the platform. These sensors are 1 to 3 axis sensors of the same type as the magnetic sensor C-1, and their number is greater than or equal to 1. Their orientation and their position may not be known precisely, which is an advantage. They are placed at a sufficiently large distance from the transmitter in the environment of the platform in order to measure as little as possible the field emitted by the emitter E. The objective is to measure the EMI present in the environment of the sensor C-1. Ideally, a single axis is sufficient but it may be necessary to place one or more sensors 1 to 3 axes close to particular equipment of the platform to measure annoying disturbances related to this or these equipment.
• FIG. 3 is a schematic view of the hardware architecture of the system according to the invention.
• the mobile body (M) is a helicopter pilot helmet, the helicopter cell forming the platform
• a calculator (4-4) receives the signals from these different components and carries out the treatments detailed below.
• FIG. 4 details the sets referred to as "blocks" and represented in FIGS. 2 and 3:
• the orientation of the mark R c with respect to the mark R M is constant and denoted by RC1 / M the matrix of the directional cosines of the axes of C1 in RM.
• the Ne components of SC form the output of this first reception set Cl.
• a calculation processor 4 for calculating the position and the orientation of the first moving object, coupled to first analog-to-digital conversion means (or ADC) 4-1 for performing the acquisition, at discrete times t k k * Te, analog signals S c , X ul and S b according to Figure 4 which will be better described later, second digital / analog conversion means E4 which generate the control of the time sequence of the currents.
• B TE vector (pseudo vector) with three components, existing at the center of the sensor is the sum of the following inductions:
• BEU B EU1 + B EU2 + B EU3 [ 2 ]
• B EMI is the vector of the induction radiated in the environment, for example generated by the currents circulating in the electrical equipment, by the generatrices of edge, by the sector 50-60Hz. " It can be modeled by the sum of periodic Bsc fields that are not correlated with B EUj and B R fields that are EMI signals whose characteristics are assumed to be random because they can not be represented by deterministic signals of known or estimated characteristics.
• B ECI is the induction vector at the center of the sensor, created by eddy currents in the conductors located in the P / O system environment, themselves produced by the magnetic field emitted by the transmitting antenna at the same time. where the drivers are.
• B FMI is the induction vector at the center of the sensor, created by the magnetization of ferromagnetic materials located in the P / O system environment.
• B T is the induction of the Earth's magnetic field.
• the induction B EU is the useful signal very strongly correlated with the emitted currents and more precisely B EU is linearly dependent on the Xu measurements of the fields emitted by the three axes El and measured according to E-3, the inductions B ECI and B FMI are also strongly correlated with the field emitted Xu.
• the method of calculating the rotation of the sensor is obtained in a known manner (US4287809 Egli): knowing Bcu, an estimation of B EU is deduced by using a model of induction in free space (without disturbances): '
• the matrix [R c / i] f pulling manner known Euler angles or quaternionQ EM are two representations of the attitude of the object M.
• Static and dynamic precision performance is obviously increasing with the S / N ratio.
• the increase in the S / N ratio sought is obtained in two obvious and complementary ways: to increase the power (or the amplitude) of the useful signal, in particular at low frequency, and to reduce the power of the noise by filtering.
• a first object of the invention is the set E which comprises according to FIG.
• a preferred embodiment consists in including in the inner volume of said El coils a very permeable magnetic material of the ferrite bar type or son of ⁇ 3 ⁇ or ferromagnetic alloy such as Vitrovac, Permalloy etc. This magnetic material as will be described later allows to multiply the magnetic induction under certain conditions of form that will be discussed.
• this set E-3 comprises a magnetic sensor for each transmission axis which measures the emitted flux and an electronic signal matching E-3-2.
• Any magnetic induction sensor (fluxgate, slave flow meter, effect sensor Hall, AMR, GMR, TMR) may also be suitable for measuring these fields.
• a preferred embodiment consists in winding coils concentrically with respect to the coils E1 to form a single fluxmeter sensor.
• a voltage amplifier E-3-2 preferably comprising a pure integration of the signals so that the magnitudes X U: j are homogeneous to a magnetic induction, provides the interface on the one hand with the acquisition system ADC 4-1 of the processor 4, on the other hand with the block E-2 which constitutes the current control device of the coils El.
• the input or setpoint of the servocontrol E-2 is the three-component signal V IC supplied by the block E-4 which is the generator of the sequence of Ne predetermined cyclic currents of periodicity Tobs.
• This block can be autonomous (memory equipped with a sequencer and containing the sequences of the current reference values) or, in a preferred embodiment indicated in FIG. 4, integrated in the processor 4.
• the values of the sequence are preferably values random binary, the sequence is called SBPA for
• FIG. 5 shows for one of the axes j the transfer functions of the blocks E1, E2, E3 of FIG. 4 which are part of the servocontrol of the emitted magnetic induction.
• XU j signals constituting the measurement of the magnetic inductions issued by El axes are subtracted from the corresponding signals V IC to form the error ⁇ of the servo itself is treated with a correction network E-2-1 which compensates, in a known manner, the transfer function of the current amplifier and especially the time constant T of the windings with magnetically permeable core El, the time constant T being close to the ratio between the inductance total L and the resistance r b of the coil.
• the transfer function of the current generator block E-2-2 takes into account these characteristics of the winding.
• the magnetic field Hi produced by the current is proportional to the number of turns per unit length n with a coefficient of proportionality K b which depends in a known manner on the geometrical shape of the coil.
• the magnetization of the nucleus is a function of the sum of Hi and the disturbing magnetic fields present in the H EMI environment.
• Effective permeability represents the term proportionality between the excitation magnetic field H j and the magnetic induction at the output, the ⁇ ⁇ magnetic field is proportional to n * I, "n" being the number of turns per unit length and I is the intensity of the current flowing in the turns of the emission coil El.
• the essential object of this servocontrol is to cancel the magnetic fields EMI present in the environment which are added to the exciter field proportional to n * I j , where I j is the current relative to the coil j, but also to linearize the coefficient ⁇ ⁇ ⁇ it is known that the magnetization of magnetic materials exhibit a nonlinear magnetization curve with saturation for strong excitation.
• ⁇ ⁇ is the effective permeability if moreover in the useful band: GF »1 [4]
• B EC is the induction produced in the center of the nucleus and ⁇ ⁇ eff the effective relative permeability.
• the signal-to-noise ratio in the kernelless and servo-free configuration is V.
• the signal-to-noise ratio is ⁇ / - B EMI .
• one of the aspects of the invention consists in producing a core in order to obtain an effective relative permeability ⁇ ⁇ eff of a few hundred units.
• the existence of ferrite cores or ferromagnetic alloy gaps exists in many applications. The latter used for example in transformers, must be laminated to reduce eddy currents that oppose magnetization and cause losses. Ferrite, much less conductive than ferromagnetic alloys, allows the use of uniform density core of this sintered material.
• the nuclei are generally spherical or cubic (or even parallelepipedal) according to FIG. 6.
• the magnetization of the permeable material of the nuclei subjected to a magnetic field excitation is a complex phenomenon because a demagnetizing field is created which opposes the field of action. excitation.
• This demagnetizing field is often explained by the creation of fictitious magnetic charges on the surface of the volumes of ferromagnetic material. It is then simply explained that the demagnetizing field is closely related to the geometry of the nucleus volume and the magnetization.
• the demagnetizing field can only be calculated for simple examples (sphere, ellipsoids, cylinders). In the general case, we make approximations. Thus for a sphere of material of relative permeability ⁇ ⁇ infinite, it is shown (CF.J.Jackson Classical Electrodynamics, Ed.Wiley) that the effective relative permeability ⁇ ⁇ eff is at most three.
• the demagnetizing field is M / 2.
• the coefficient, less than unity, takes into account several factors, including:
• very thin bars of permeable material are used, for example previously electrically insulated ⁇ -ietal, permalloy or Vitrovac wires, arranged according to FIG. 7-1 in a tube of resistant material. thermal treatments (silica, ceramic).
• the bars are grouped together (FIG. 7-2) to form a block of square section (FIG. 7-3) or cylindrical section (FIG. 7-4) comprising a large number of bars.
• These blocks 7-3 and 7-4 are arranged so as to form three volumes of orthogonal magnetization materials and having a symmetry with respect to the center common to the three axes.
• Figure 8-a shows how the assembled blocks of Figure 7-3 or 7-4 can be used: three coils are made around three identical blocks which are then mechanically assembled to form three substantially perpendicular axes. These three coils are not concentric, which poses significant difficulties to find the position of the three-axis sensor fixed on the object whose position and orientation is sought. We will therefore prefer to realize concentric emitter blocks according to Figures 8-b and 9.
• Figures 8-b preferable configurations of blocks are shown so that there is a center of symmetry of the three magnetized volumes and each axis has a magnetic moment. of neighboring value.
• FIG. 4 shows two views in projection of a preferred device which is a generalization of the preceding blocks: several blocks of type 2-3 are interwoven in the three directions so that there is the best symmetry with respect to a point central.
• a cubic block is obtained according to FIG. 9 on which there are three substantially orthogonal coils through which the currents injected by the electronic circuits will pass. So that the magnetic induction vector behaves in space according to the equations of the dipole, it remains in the invention by realizing a block whose outer surface is close to a sphere, with blocks 7-3 or 7-4 shorter in length when moving away from the center.
• a device consisting in producing three concentric spherical coils instead of the concentric cubic coils of FIG. 9, and introducing the same entanglement of blocks of type 7-3 or 7-4 in the volume of the inner coil remains in the range of the invention.
• FIG. 10-a shows the principle of operation: when a static or quasi-static field Hext is present in the environment, its projection H D along the emission axis El shifts the operating point of the alternating excitation field H ⁇ produced by the coils according to scheme 10-b.
• the operation of the impedance variation which deforms the current is carried out by the detection of the symmetry of the current flowing in the coil:
• the output V CRJ of E.5.1 is then added to V Icj with the sign adapted in the winding direction so as to cancel the field shift H D.
• the symmetry of the current could also be detected by the creation of even harmonics of the current knowing that the excitation Hi, symmetrical, possesses only odd harmonics.
• Block 4.3 receives from a conventional serial digital link that communicates with the inertial system of the platform, the dated information with respect to the own clock of 4 is constituted. This allows, if necessary, to adjust the attitudes of the platform temporally. This block also receives the serial type digital information from the MEMS C-3.1 inertial sensor.
• B TE B EU + B EMj + B ECI + B j y jj + B T [7] the useful signal B EU is linearly dependent on the signals emitted by the transmitter block E.
• the fields emitted by the axes El are measured by the block E3 previously described whose output is XU j .
• XU j is the image of the magnetic field emitted by the axis j regardless of the nonlinear amplification function provided by the magnetic cores.
• B pcu B ECI + B FMI (PCU for perturbations correlated with U) are correlated noises with Xu.
• the terrestrial field is supposed to be filtered by a known conventional filter not forming part of the invention.
• the EMI additive noises for a particular embodiment of the invention, they are measured by block C-2: as indicated in FIG. 3, block C-2 is fixed in the platform P, comprising a plurality of sensors located at points such that i) the field emitted by the set E1 is almost zero or at least much smaller than the point contained in the deflection volume of the sensor, where Cl is located of the moving set M, ii) the disturbing fields statistically uncorrelated with the fields emitted by El and existing at the center of the sensor C1 are very strongly correlated with these fields measured by C-2.
• the B EMI noise is lower than in helicopter environments and especially noise B R is very low. In this type of environment, it may be necessary to extract the noise instead of measuring it.
• the definition of block 4.4 then allows a reference noise extraction method B ⁇ t ⁇ in two different ways:
• First method either an extraction directly from the signal Se (obtained by the acquisition of the signal provided by the first set of measurement C1). In this case, this choice is made by the processor in block 4.4 depending on the nature of the magnetic noise. This choice results from an initial analysis of the magnetic noise of the environment at power up or at the request of the user. For example, at power up, in the absence of signals emitted by the transmitting antenna, if the average power density values of the measured signals are harmonic and of acceptable frequency stability (variation of 10 to 20% maximum of the average frequency) and lower than the average power density level of the signals due to the emission of the transmitting antenna when it emits, this choice is made . This choice can also be made by the user following the accumulation of experience he has obtained from the environment or any other means.
• This choice requires the transmission power to be zero during a period of duration T off , this period T off being interleaved between at least one emission period of duration T obs with non-zero power, with T off ⁇ T obs / 2 .
• T off is interleaved between at least one emission period of duration T obs with non-zero power, with T off ⁇ T obs / 2 .
• T 0FF the stationary disturbing signals (weakly variable on T 0BS ) are identified in the same way as that which will be described for the extraction of these same signals on the signal Sb.
• the model of these signals B sc or B ESC (the letter E indicates that this vector is expressed in the emitter reference)
• X c (j, k i , t k ) are the time-shifted values of the fields emitted by the transmitter on each axis j and for each component i c of the block C1 sensor.
• the estimator is in a transverse filter which is justified by the fact that the disturbances ECI and FMI can be considered as the output of substantially first-order filters whose input are the signals X (t k ) ⁇
• K lc are related to the delays of the variables independent of the model and go from 0 to Ni c , the latter index N lc being defined just necessary in order to minimize the residual error.
• the offset terms of K 1c form a transversal filter.
• B m is written as a development of comlex variables: C sc (i c , k sc ) ⁇ X sc (t t ) [12]
• Equations [11] and [12] which are linear with respect to the parameters to be estimated.
• the parameters of this model are determined by a classical least squares (MSE) method or an equivalent recursive method (LMS, RLS).
• MSE classical least squares
• LMS equivalent recursive method
• the estimation of the parameters relating to the variables XU j can be refined by subtracting the estimated term B sc (i c , t k ) from the signal Sc (i c , t k ).
• the new estimate makes it possible to estimate the correlated terms with a better accuracy after one or two iterations.
• the reference noise is in this case the signal sc estimated in the previous iteration.
• Second method The continuous measurement of the disturbing signals by S b may be indispensable in the presence of very strong harmonic signals of non-constant amplitudes and frequencies on the Tobs horizon but also in the presence of non-stationary deterministic perturbations or random perturbations. This is an estimate of the signals radiated by the measurement of the signals S b . As has been written and illustrated in FIG.
• a noise reference B RM t k
• the measurements of the additive noise B EMI are indicated by the output signals S b of the block C-2 on the plate 4.
• Nb 1 and we will consider that the measurement of only one component is enough.
• the measurement of E RM (t k ) in a particular direction will be noted to be considered as a signal highly correlated with B EMI .
• B RM is not negligible as in i) and it is to extract from [13-a] part B RM .
• all the terms of the model must be identified in order not to bias the estimation of the parameters of the model.
• the random signal B R is generally lower that B sc and B cu , and the identification can be performed over longer times since the C-2 sensors are immobile.
• the identification of the parameters of the model [14] can be made once and for all or at the beginning of the use of the system during an initialization phase of sufficient duration to allow a very good precision in the estimation of the parameters following the filtering of the terms of [14] which are not correlated with [14]. This identification is exactly the same as that described in [10], [11], [12].
• the parameters of [14] are then stored for the calculation of B CU .
• the principle of B RM extraction is to write:
• BRM B C2 ⁇ BRU [16-a] where è RU are the estimates of the signals correlated with XU j .
• B RM of [16-a] is therefore the estimate of the uncorrelated noise with the transmitted fields. It is thus seen that, when signals are transmitted by E1, in the two embodiments i) and ii) described above, the same model had to be identified on the measurements Se (coming from block Cl) or S b (coming from block C-2).
• E indicates that the vector is expressed in the reference of the issuer (this index is sometimes omitted by simplifications knowing that the context indicates in which frame the fields are expressed), u indicates that it is the part of the field linearly dependent on the fields emitted by the transmitter Xu.
• the index Cu indicates that B CU / E ⁇ B ECI + B FMI represents the vector of perturbations correlated with the vector X ".
• B ⁇ has the same meaning as in [13] and [15], it is the noise present in the environment uncorrelated with the emitted fields.
• Neglected B T which is supposed to be filtered by a conventional digital filter known to those skilled in the art.
• the three models are developed linearly with respect to parameters to be identified, for example, by a standard method of minimizing the quadratic error.
• the fundamental interest of this complete modeling of the signals received by the sensor Cl resides in the fact that the 9 parameters of A are all the less biased that the independent variables of the model represent the most exactly the physical phenomena.
• Model B U / E Subsequently, it is considered that the sensor C1 has been corrected for its errors according to the known methods: the functions of gain correction, misalignment, etc., are applied. Assuming that the distance between the sensor C1 and the emitter is at least three times the largest dimension of the emitter, it is then written in a known manner that the model is of the dipolar type and is written
• D c / E is the distance between the center 0 C of the sensor C1 and the center of the transmitter CL:
• DC / E is variable with time, such as rotation
• m l m 2 , m 3 are the multiplicative terms of amplitudes of the magnetic moments that depend on the selected units, the gains of the current amplifiers E-2, ⁇ ⁇ , ⁇ ⁇ , ⁇ ⁇ the coefficients
• the V E3 output of the E-3 sensors is either digitized by the CAN block of the processor for the three axes and digitally integrated or according to a preferred mode according to Figure 4, it is first integrated by an analog amplifier E-3 2 then digitized by the CAN block 4-1 of the processor 4 and each of the channels is normalized by a coefficient determined in the factory in a manner known to those skilled in the art, so that the values thus standardized correspond to the physical units and their nominal values.
• the coefficients ⁇ ⁇ , ⁇ ⁇ , ⁇ ⁇ are determined in the factory by bench calibration procedures by factory methods known to those skilled in the art.
• Bc (t) (A 21 1 + ⁇ 22 ⁇ ! + A 23 Y 1 ) m 1 f 1 (t) + (A 21 a 2 + ⁇ 22 ⁇ 2 + A 13 Y 2 ) m 2 f 2 (t ) + (A 21 a 3 + ⁇ 22 ⁇ 3 + A 33 Y 3 ) m 3 f 3 (t) 25] (A 31 0 ! + ⁇ 32 ⁇ !
• the two matrices, C E and K E (gains and misalignment) relative to the transmission block El, are identified at the factory, and the desired matrix A is then easily obtained.
• a composed of the coefficients of the functions x cu [ul x, x U2, U3 x] t was thus produced demultiplexing the transmission paths by identifying a model, and not by a temporal demultiplexing (non-simultaneous program ), nor a frequency demultiplexing (US6754609 Lescourret, US 6172499 ASHE, etc.) or any other demultiplexing.
• B cu / E can be considered as the output of a linear filter whose input are the inductive fields emitted by El, and the output is the measurement by the sensor Cl. It is therefore always possible consider that the output at instant t k is a linear combination of inputs at instants t ⁇ k ⁇ Te. If we note:
• the number of coefficients and the number of variables are Ne * Max / lc (N (i c )).
• a cu (i c , j, 0) are the terms of the model in free space that is to say without disturbers.
• one of the objects of the invention is to compensate the latency of a position / orientation detection system.
• the example described relates to a magnetic system but would apply to any system for detecting the orientation of a moving body.
• One aspect of the invention is to associate magnetic detection with an inertial system whose excellent properties are known in the short term, that is to say a very short response time, but having long-term drifts, in particular due to bias and bias drifts.
• the Magnetic Position Detection means has excellent long-term stability but a response time related to the signal-to-noise ratio which may be insufficient under certain conditions.
• the principle of the invention is to associate, it is also said to hybridize, the magnetic system and the inertial system, when the platform has a central inertia providing at all times the attitude of the platform in a fixed Galilean landmark.
• Figure 12-a shows the state of the art of using the angular velocities measured on the moving object and also on the platform to be processed in a KALMAN filter.
• FIG. 12-b describes the principle of the invention which consists in measuring the angular velocities of the moving object M, and integrating them numerically in known manner from the time t L (initial time) to the time t f (final time) to obtain the rotation of the mobile between these two instants in the fixed reference.
• the acquisition of the angular velocities is done by the block C-3-1 of FIG. 3, composed of a MEMS sensor delivering the angular velocities digitized to clean rate T g which is a sub multip of the c ⁇ o. bs : ⁇ g / k, k
• gg is a positive integer
• t. is for example the fraction of time following the arrival time of the information of the magnetic position detecting means t n replenisht.
• t f is the moment for which the information is desired. In the invention, there are two particular moments t f . The first is the instant t the second is the instant t n + T obs . This will be better understood later.
• This rotation is R TM (t n ) that is to say the rotation of the axes of the reference mark R M linked to the moving object M according to Figure 2 expressed in the reference of the transmitter.
• R EM R P / I R MP
• R p / I which is none other than the director cosine matrix of the platform which is provided by the inertial unit C-3- 2 of the platform, usually in the form of the three angles of Euler Gisement ⁇ , Site ⁇ and roll ⁇ , from which we calculate R p 1 / I 1 then R E M M / I.
• this initial condition is the value of the state predicted by the model at t n plus a fraction of the error between the estimated measure and the actual measure.
• ⁇ ⁇ + ⁇ ⁇ [34]
• ⁇ b a random bias and Kla matrix of the errors of gain, misalignment and coupling between channels.
• the propagation of the gyrometric errors is carried out by a dynamic model of the terms of ⁇ co, itself integrated as it is known to do with a KALMAN filter.
• dQ the error between the value Q M (t n ) calculated by the means of magnetic position detection at time t n and Q (t n ) integrated t t n
• the error propagation state vector is an example of the type
• v, Vg, Vk are supposedly Gaussian additive noises centered on the characteristics of the fluctuations of the terms b ro and K of [38-a and 38-b] and the error provided by the magnetic detection system.
• Equations [35] to [38] can be numerically integrated in a variety of ways or put into the form of recursive matrix equations.
• the parameters of ⁇ are recalculated by formulas known to those skilled in the art depending on the filter chosen, for example the KALMAN filter.
• the gain control is not part of the invention, in particular because it depends a lot on the experimental conditions (noise, quality of the sensors, etc.).
• the latency compensation is carried out in the following way: After resetting the filter according to [41] at the moment we integrate the equations [35] to [38] over a time t kg -T obs / 2 until kg (the current time), using the raw angular velocities stored over this time interval, and corrected according to [33-d].
• the initial value of Q is the value recaled to t ".
• the matrix defining the direction cosines of the reference point of the moving object M with respect to the reference reference point (reference point of the platform R p ) is then calculated by the expression
• R m / p (' k8 ) 3 ⁇ 4 / ⁇ ( ⁇ ) 3 ⁇ 4 / ⁇ ( ⁇ ) 3 ⁇ 4 / ⁇ .
• the second orientation can be defined by the Euler angles extracted from the matrix R m / p (t 3 ⁇ 4 ) by formulas known to those skilled in the art.
• This method makes it possible firstly to provide at a very high rate (of the order of 10 times higher) the estimate of the second orientation, which minimizes the delay between the supply of the calculated information and its use by the system which in fact the acquisition at any periodicity and unsynchronized with t n , and secondly the compensation of latency by calculating the trajectory of (t kg -Tobs / 2) to t kg thanks to the memorization and their correction of gyro velocities from (t kg -Tobs / 2) to t kg .
• the applications of the invention are essentially those for which a high accuracy is necessary for the position and orientation of a body with respect to another body taken for reference in the presence of strong electromagnetic disturbances.
• the position and orientation of the civilian and military aircraft pilots helmet without using magnetic mapping is a first application. Many applications in surgery, simulators, motion capture and video games, etc. are possible.

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