Navigation device and method using correction data in a remote imu

Abstract

The invention relates to a navigation device (1), comprising an inertial measurement unit (100) and an electronic navigation computation unit (200) connected to each other by a data link (300), the inertial measurement unit (100) comprising inertial sensors (110, 120) for producing location signals and the electronic navigation computation unit (200) being arranged to compute a navigation from the location signals, characterised in that the inertial measurement unit (100) includes an electronic processing circuit (130) connected to the inertial sensors (110, 120) and provided with a memory containing an error model of the inertial measurement unit; in that the electronic processing circuit is arranged to transmit to the electronic navigation unit, at a first rate, the location signals as well as, at a second rate, correction signals comprising first correction data that are representative of an impact of the errors of the sensors on the location signals over a given period and which are determined by the electronic processing circuit from the error model, and second correction data that are representative of an effect of the noises and random errors of the inertial measurement unit over the given period; and in that the electronic navigation computation unit implements a hybridised navigation algorithm arranged to provide a hybridised location which is based on inertial location data extracted from the location signals and the external location data and which is readjusted using the correction data.

Description

[0001] NAVIGATION DEVICE AND METHOD USING CORRECTION DATA IN A REMOTE UMI

[0002] The present invention relates to the field of inertial measurement units and more particularly to inertial navigation systems allowing navigation based on measurements provided by at least one inertial measurement unit.

[0003] BACKGROUND OF THE INVENTION

[0004] Inertial navigation systems are known, an example of which is shown in FIG. 7 under the general reference 1000, comprising, in the same housing, an inertial measurement unit 1100 connected by a data link to an electronic navigation calculation unit 1200.

[0005] The inertial measurement unit 1100 comprises accelerometers and angular sensors arranged along the axes of a measurement frame [m] to provide primary signals representative of the integral, over a time step (for example between an instant t i -1 and a time t i), of the specific force vector and of the angular velocity vector relative to an inertial reference frame [i]. The successive signals are thus representative of the integral of the specific force vector on the one hand and of the angular velocity vector on the other hand from an instant t0 to an instant ti, then from an instant ti to an instant t2, then from an instant t2 to an instant t3, etc.: the signals are therefore generally called increments. The specific force (in English "specific force", "g-force" or "mass-specific force") is a representation of the sum, on the one hand, of the acceleration of the carrier of the inertial measurement unit relative to the inertial frame and, on the other hand, of the Earth's gravity.The electronic navigation calculation unit 1200 comprises a processor and a memory containing a navigation computer program which is executed by the processor and which uses the signals provided by the inertial measurement unit 1100 to determine a trajectory of the carrier (a vehicle) carrying the navigation system. Since the primary signals provided by the inertial measurement unit 1100 are increments indicative of a variation in the location of the carrier and not an absolute value, the navigation calculations must be carried out at a high rate, typically 50 to 200 Hz, in order to ensure an accurate reconstruction of the location which is insensitive to the dynamics of the carrier. A clock 1001 makes it possible to synchronize the inertial measurement unit 1100 and the electronic navigation calculation unit 1200.

[0006] It is understood that a loss of signal, even of short duration, between the inertial measurement unit and the electronic navigation calculation unit is very detrimental since part of the increments are not used.

[0007] To improve navigation accuracy, consideration has been given to using more expensive inertial sensors, optimizing electronic signal processing, using more reliable data links between the inertial measurement unit and the electronic navigation unit when they are distant, etc.

[0008] It is also known to use external location data, for example from a satellite navigation system (so-called GNSS systems such as GPS, GALILEO, GLONASS, BEIDOU, etc.), an aerodynamic data computer (baro altimeter, pitot, etc.), a stargazing device, etc. These external data are then used periodically to initialize or recalibrate inertial navigation. This is referred to as the alignment or harmonization phase (alignment of a ship at the dock) and hybrid navigation.

[0009] SUBJECT OF THE INVENTION

[0010] The invention aims in particular to improve the performance of hybrid navigation.

[0011] SUMMARY OF THE INVENTION

[0012] For this purpose, a navigation device is provided, comprising an inertial measurement unit and an electronic navigation calculation unit connected to each other by a data link. The inertial measurement unit comprises inertial sensors for producing location signals and the electronic navigation calculation unit is arranged to calculate a navigation from the location signals. The inertial measurement unit comprises an electronic processing circuit connected to the inertial sensors and provided with a memory containing an error model of the inertial measurement unit.The electronic processing circuit is arranged to transmit to the electronic navigation unit, on the one hand, at a first rate, said location signals and, on the other hand, at a second rate, correction signals comprising first correction data which are representative of an impact of the errors of the sensors on the location signals over a given period and which are determined by the electronic processing circuit from the error model, and second correction data representative of an effect of the noises and random errors of the inertial measurement unit over the given period. The electronic navigation calculation unit implements a hybrid navigation algorithm arranged to provide a hybrid location which is based on inertial location data extracted from the location signals and external location data and which is realigned from the correction data.

[0013] “Location signals” are signals comprising location data enabling the vehicle’s location to be calculated. Thus, the electronic processing circuit is able to provide the electronic navigation calculation unit with the location signals and the correction signals enabling the electronic navigation calculation unit to develop a corrected hybrid navigation and therefore to have better performance, particularly for real-time implementation, for example, of several hybridizations and navigations associated in parallel.

[0014] Preferably, the electronic processing circuit is arranged to perform at least a first integration, as a function of time, of primary data contained in primary signals from the inertial sensors over an integration duration, which begins at a single integration start instant and which is measured, to produce processed data inserted into signals forming the location signals with time information representative of the integration duration, and in that the electronic navigation calculation unit is arranged to extract the processed data and the time information from the location signals and use them to calculate the navigation taking into account the integration duration.

[0015] It is no longer the primary signals (the increments produced by the inertial sensors) which are transmitted at high speed to the electronic navigation calculation unit as in the prior art, but values ​​integrated over an unbounded integration time, from the single integration instant (the same for all the processed data, corresponding for example to the start-up of the system or to the reception of a command to start integration), which can be transmitted at the same speed or at a lower speed. It is understood that the location signals successively sent by the electronic processing circuit will be representative of an integration from time t0 to time ti, then from time t0 to time t2, then from time t0 to time t3, etc. In this way, whatever the time at which a location signal is received, it is representative of an integration from the single integration start instant.The navigation error in the event of a failure to receive one or more data frames is greatly reduced compared, for example, to a conventional method consisting of carrying out an extrapolation from conventional speed and angle increment data received before and after the transmission failure. The transmission of data according to the invention is therefore less restrictive while limiting the consequences of a transmission error. The processing of the data to form the location signals which will be transmitted therefore makes the transmission of the data and the navigation calculation carried out from said data more reliable. Such transmission is advantageous at short distance but also at relatively long distances (several meters).

[0016] Advantageously, the electronic processing circuit is arranged to:

[0017] - carry out a first integration of at least part of the primary data, a second integration on the result of the first integration, and a third integration on the result of the second integration;

[0018] - calculate, from the results of the first integration and the results of the second integration, a transition matrix from the inertial frame to the navigation frame in the form of a first matrix composed of the coefficients of the Legendre polynomials of order 0 and a second matrix composed of the coefficients of the Legendre polynomials of order 1;

[0019] - calculate, from the result of the third integration, the coefficients of the Legendre polynomials of order 2 of a third matrix added to the sum of the previous ones to refine the calculation of the transition matrix.

[0020] The invention also relates to a method of navigation by means of a navigation device comprising an inertial measurement unit and an electronic navigation calculation unit connected to each other by a data link, comprising the steps of

[0021] - in the inertial measurement unit:

[0022] . develop location signals from inertial sensor measurements and transmit the location signals to the navigation computing electronics unit at a first rate,

[0023] . from an error model of the inertial sensors recorded in the inertial measurement unit, developing correction signals comprising first correction data which are representative of an impact of the errors of the sensors on the location signals over a given period, and second correction data representative of the evolution noises representative of the errors of the model over the given period, and transmitting the correction signals to the navigation calculation electronics unit at a second rate; and

[0024] - in the electronic navigation calculation unit: by means of a hybrid navigation algorithm, calculating a hybrid location which is based on inertial location data extracted from the location signals and external location data,

[0025] . recalibrate the hybrid localization from the correction data.

[0026] More specifically, in a preferred embodiment, the electronic navigation unit is arranged to:

[0027] • calculate, at a low rate (i.e. lower than the rate of transmission of the location signals) the evolution of a hybrid location which is based on inertial location data, current errors of the inertial measurement unit estimated by the hybrid navigation algorithm and the first correction data;

[0028] • calculate, at low speed, the evolution of the error statistics of the hybridized navigation and the errors of the inertial measurement unit (for example in the form of a covariance matrix for hybridization by a Kalman filter), from the inertial location data, the current errors of the inertial measurement unit estimated by the hybridized navigation algorithm, the first and second correction data;

[0029] • recalibrate, at low cadence, the estimated errors of inertial navigation and the inertial measurement unit, with the location data at the time of recalibration and, preferably, externally available dated data to improve location accuracy.

[0030] More preferably, the first correction data are the components of the inertial localization error evolution matrix PHI and the inertial measurement unit at the low rate and the second correction data are the components of the inertial localization error random evolution matrix Q and the inertial measurement unit at the low rate. The Q matrix is ​​also commonly referred to as the desensitization matrix or noise matrix.

[0031] The invention finally relates to a vehicle equipped with a navigation device according to the invention.

[0032] Other characteristics and advantages of the invention will emerge upon reading the following description of a particular and non-limiting embodiment of the invention.

[0033] BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Reference will be made to the attached drawings, including:

[0035] [Fig. 1] Figure 1 is a partial schematic view of an aircraft equipped with a navigation device according to the invention;

[0036] [Fig. 2] Figure 2 is a schematic view of the device according to the invention;

[0037] [Fig. 3] Figure 3 is a flowchart showing the data exchanges during the implementation of the method according to the invention;

[0038] [Fig. 4] Figure 4 is a flowchart showing the implementation of the method according to the invention, on the inertial measurement unit side;

[0039] [Fig. 5] Figure 5 is a flowchart showing the implementation of the method according to the invention, on the electronic calculation unit side for processing the location signals; [Fig. 6] Figure 6 is a flowchart showing the implementation of the method according to the invention, on the electronic calculation unit side for processing the correction signals;

[0040] [Fig. 7] Figure 7 is a flowchart showing the data exchanges in a navigation device according to the prior art. DETAILED DESCRIPTION OF THE INVENTION

[0041] With reference to the figures, the invention is described here in an aeronautical application, the navigation device of the invention being on board an aircraft A having a structure comprising a fuselage and wings and having a center of gravity G.

[0042] The navigation device according to the invention, generally designated 1, comprises an inertial measurement unit 100 and an electronic navigation calculation unit 200 connected to each other by a data link 300. The inertial measurement unit 100 is here positioned substantially at the center of gravity G of the aircraft A and the electronic calculation unit 200 is here positioned at the front of the aircraft A, in an avionics bay B grouping together the computers used for processing the data used for piloting the aircraft A. Thus, the inertial measurement unit 100 is arranged at a first distance from the center of gravity G and the electronic navigation calculation unit 200 is arranged at a second distance from the center of gravity, the first distance here being less than the second distance. The difference between the first distance and the second distance is here several meters.

[0043] The inertial measurement unit 100 comprises a first housing 101 containing inertial sensors, namely linear inertial sensors (more precisely accelerometers 110) arranged along the axes of a measurement frame [m] to measure the “gravitational speed” of this frame (i.e. the time integral of the specific force present at the center of this frame) and angular inertial sensors, here gyrometers 120, arranged along the axes of this frame to measure the rotation of the measurement frame [m] relative to an inertial frame [i]. The inertial sensors do not provide absolute values ​​but increments representative of a variation of the measured quantity compared to the previous measurement. The increments of the integral of the specific force are thus representative of a variation of the components of the gravitational speed along the three axes of the frame [m].The rotation increments are thus representative of the variation of the integral over time of the angular rotation speed of the measurement frame [m] with respect to the inertial frame [i] and are provided in the form of quaternions (rotation quaternion Qi / m of passage from [m] to [i]), Euler angles, rotation matrices, or Bortz vectors. The inertial sensors thus provide first signals or primary signals containing first data representative of a variation in gravitational speed (accelerometric measurement) and second data representative of an angle variation (gyrometric measurement). Conventionally, these signals are provided at a rate of between 100 Hz and 400 Hz.

[0044] The first housing 101 is received in a second housing 102 of the inertial measurement unit 100. The second housing 102 also contains an electronic processing circuit 130 having inputs connected to the outputs of the inertial sensors 110, 120 for example by electrical conductors such as printed circuit tracks or cables. The electronic processing circuit 130 here comprises at least one processor and a memory containing a first computer program which is executable by the processor and which comprises instructions arranged to implement the method of the invention. This first program will be detailed later.

[0045] The electronic navigation calculation unit 200 is known per se and comprises a housing 201 containing at least one processor and a memory containing a second computer program which is executable by the processor and which comprises instructions arranged to implement the method of the invention. In general, the electronic navigation calculation unit 200 is arranged to calculate a navigation from signals supplied by the inertial measurement unit 100. This second program will also be detailed later.

[0046] The inertial measurement unit 100 and the electronic navigation calculation unit 200 each have a clock enabling the former to date the signals transmitted and the latter to date the times of reception.

[0047] The inertial measurement unit 100 and the electronic navigation calculation unit 200 are physically separated from each other but are connected to exchange signals. Thus, the electronic processing circuit 130 has at least one output connected to at least one input of the electronic navigation calculation unit 200 by a data link 300. The data link 300 is here an Ethernet link for example compliant with the ARINC664 standard.

[0048] The inertial measurement unit 100 is arranged to provide the electronic navigation calculation unit with two types of signals: location signals and correction signals which will be successively detailed below. The development of the location signals is first detailed below.

[0049] More precisely, the first program provides location signals at times t iaccording to a first cadence and location signals at times t k according to a second cadence, here lower than the first cadence.

[0050] The first program executed by the electronic processing circuit 130 receives as input the first signals containing the first data and the second data. To form the location signals at t1, the first program is arranged to perform: - a first integration, over an integration duration measured from a single integration start instant t0 (duration noted t e -t0 in figures 3 and 4, i varying from 0 to e), second data to produce second integrated data;

[0051] - a projection of the first data into the inertial frame [i] to obtain first projected data;

[0052] - a first integration of the first projected data, over the integration duration measured from the single integration start time t0, to produce first integrated data;

[0053] - a first shift (Shift V or SHV) of the first integrated data to obtain first processed data (the first shift is carried out when the value of the first integrated data exceeds a range of values ​​acceptable for their subsequent processing);

[0054] - a second integration of the first processed data, over the integration time measured from the single integration start time t0, to produce first doubly integrated data;

[0055] - a second shift (Shift P or SHP) of the first doubly integrated data to obtain first doubly processed data (the second shift is carried out when the value of the first doubly integrated data exceeds a range of values ​​acceptable for their subsequent processing).

[0056] The inertial reference frame [i] is for example the measurement reference frame [m] at the time of powering up the inertial measurement unit 100 or any other inertial reference frame angularly offset relative to the latter and for example the reference frame [m] at the instant of start or end of integration. The first program executed by the electronic processing circuit is arranged to calculate the integrations in floating or fixed point with a number of mantissa bits making it possible to achieve the required localization precision with a minimum time between two successive offsets of 20s. A double precision calculation on 64 bits including 48 mantissa bits makes it possible to achieve a precision objective of for example 0.001 ms -1 , 0.001 m, 0.001° / h and 1 rad.

[0057] We understand that:

[0058] - the second integrated data are representative of an angular position (or an orientation);

[0059] - the first integrated data and the first processed data are representative of a linear speed;

[0060] - the first doubly integrated data and the first doubly processed data are representative of a linear position.

[0061] The first shift operation comprises the step of comparing an absolute initial value of each component of the first integrated data to at least a first threshold Svitesse. When the components of the first integrated data have absolute current values ​​below the first threshold, the first program leaves the current values ​​unchanged, which amounts to applying a zero shift. When one of the components of the first integrated data has an absolute current value reaching or exceeding the first threshold, the first program applies to said component of the first integrated data a predetermined shift to bring said component of the first integrated data to a shifted value below the first threshold.In other words, a first SHV ​​offset value (equal here to the first threshold) is deduced from the initial value of said component of the first integrated data (or added to it according to the sign of the current value) to obtain the offset value. This makes it possible to maintain the value of each component of the first data in a range of values ​​[-Sspeed; +Sspeed]. The first threshold Sspeed is determined according to an expected speed resolution for navigation. The integration time without offset obviously depends on the dynamics of the aircraft A. The first integrated data and the first SHV ​​offset value are expressed here in meters per second.

[0062] The second shift operation comprises the step of comparing an absolute current value of the first doubly integrated data to at least a second threshold Sposition. When the components of the first doubly integrated data have absolute current values ​​below the second threshold, the first program leaves the current values ​​unchanged, which amounts to applying a zero shift. When the value of one of the components of the first doubly integrated data reaches or exceeds the second threshold, the first program applies to said component of the first doubly integrated data a predetermined shift to bring said component of the first doubly integrated data to a shifted value below the second threshold.In other words, a second SHP offset value (equal here to the second threshold) is deduced from the initial value of the first doubly integrated data (or added according to the sign of the initial value of said component) to obtain the offset value. This makes it possible to maintain the value of each component of the first doubly integrated data in a range of values ​​[- Sposition ; +Sposition]. The second threshold Sposition is determined according to an expected resolution in position for navigation. The integration time without offset depends on the dynamics of the aircraft A and the threshold Svelocity. The first doubly integrated data and the second SHP offset value are expressed here in meters.The first processed data (which correspond to the three components of the speed including the integration of the effect of gravity, possibly affected by a shift, and for this reason called pseudo-speed PV or pseudo-inertial speed PVI), the first doubly processed data (which correspond to the three components of the position including the double integration of the effect of gravity, possibly affected by a shift - speed or position - or by two shifts - speed and position, and for this reason called pseudo-position PP or pseudo-inertial position PPI), the second processed data (which correspond to the three components of rotation representative of the attitude of the aircraft A), and time information (an integration step counter or time step of the inertial measurement unit between the sampling instant and the single instant of start of integration, here t. e-t0) are put in the form of a packet introduced into second signals at t transmitted via the data link 300 to the electronic navigation calculation unit 200. These second signals at t i are the location signals at t i (also called pseudo-inertial localization signals). To form the localization signals at t k , the first program is arranged to perform:

[0063] - a first integration, over an integration time measured from the previous instant t k-1 (duration noted t k-1 -t k in Figures 3 and 4), second data to produce second integrated data;

[0064] - a projection of the first data into the inertial frame [i] to obtain first projected data;

[0065] - a first integration of the first projected data, over the integration time measured from time t k-1, to produce first integrated data; - a second integration of the first integrated data, over the integration time measured from time t k-1 , to produce first doubly integrated data;

[0066] - a third integration of the first integrated data, over the integration time measured from time t k-1 , to produce the first doubly integrated data.

[0067] We thus obtain a batch of location data of t k-1 to t k in which:

[0068] - the second integrated data of t k-1 to t k are representative of an angular position increment (or an orientation);

[0069] - the first integrated data of t k-1 to t k are representative of a linear speed increment;

[0070] - the first doubly integrated data of t k-1 to t kare representative of a linear position increment;

[0071] - the first triple integrated data of t k-1 to t k serve to improve accuracy as we will see later.

[0072] The location signals at t k may also include:

[0073] - a first integration, over an integration time measured from the single integration instant t0 (i.e. t k -t0), second data to produce second embedded data;

[0074] - a projection of the first data into the inertial frame [i] to obtain first projected data;

[0075] - a first integration of the first projected data, over the integration time measured from the single integration instant t0, to produce first integrated data; - a first shift (Shift V or SHV) of the first integrated data to obtain first processed data (the first shift is carried out when the value of the first integrated data exceeds a range of values ​​acceptable for their subsequent processing);

[0076] - a second integration of the first processed data, over the integration time measured from the single integration start time t0, to produce first doubly integrated data;

[0077] - a second shift (Shift P or SHP) of the first doubly integrated data to obtain first doubly processed data (the second shift is carried out when the value of the first doubly integrated data exceeds a range of values ​​acceptable for their subsequent processing).

[0078] The offsets are based on the same principle as those previously described.

[0079] We thus obtain a batch of location data from t0 to t k in which:

[0080] - the second integrated data from t0 to t k are representative of an angular position (or an orientation);

[0081] - the first integrated data from t0 to t k are representative of a linear speed;

[0082] - the first doubly integrated data from t0 to t k are representative of a linear position.

[0083] The location data set of tk-1 to t k and batch of location data from t0 to t k , as well as time information for the latter (an integration step counter or time step of the inertial measurement unit between the sampling instant and the integration start instant, here t k -t0) are put in the form of a packet introduced in second signals at t k transmitted via the data link 300 to the electronic navigation computing unit 200. These second signals to t k are the location signals at t k .

[0084] The second program executed by the electronic navigation calculation unit 200 is arranged to extract, from the second signals at ti, the processed data and the temporal information and implements an inertial navigation algorithm to use them to calculate the inertial location taking into account the evolution of the integration time since the last extraction of the second signals.

[0085] More precisely, with reference to Figure 5, the second program receives as input the second signals at t i , in the form of two data packets sent at each time t iby the first program but recovered respectively for example at time ti then at time t2 each comprising the first processed data, the first doubly processed data, the second processed data, and the time information corresponding to the sampling time of the pseudo-navigation data in the inertial measurement unit with any internal drifts of the clock of the inertial measurement unit (this time information is a number of integration steps of the inertial measurement unit, from the single integration start time t0, associated with the data packet emitted by the inertial measurement unit). The two times t1 then t2 are separated by less than half the minimum time between two successive shifts of a pseudo-velocity or pseudo-inertial position component.

[0086] Considering for the simplicity of the description that the data received at time ti have already been used, the second program must carry out the operations allowing calculation from the data received at time t2:

[0087] - the three components of variation of the pseudo-inertial velocity from ti to t2 in the measurement frame [m], noted DVm(t1->t2), corrected for the effect of an SHV shift;

[0088] - the three components of variation of the pseudo-inertial velocity from ti to t2 in the inertial frame [i], noted DVi(t1->t2), corrected for the effect of an SHV shift;

[0089] - the three components of variation of the pseudo-inertial position from ti to t2 in the inertial frame [i], noted DP(t1->t2), corrected for the effect of an SHP shift;

[0090] - the three components of correction of the pseudo-inertial position of ti at t2 in the inertial frame [i], noted CorrPPi(t1->t2),

[0091] - a logic indicator ShiftPVdetected for detecting a shift of at least one of the pseudo-speed components between t1 and t2.

[0092] We recall that the data received at time ti and the data received at time t2 have been integrated since the start of integration time t0. It is therefore sufficient to subtract the data received at time ti from those received at time t2 to obtain the data corresponding to the time interval t2-t1. The rate dt k =t2-ti determines the calculation accuracy of the evolution of the inertial position and attitude from tl to t2. The error due to the sampling rate is mainly generated in the variable acceleration phase. It is equivalent to approximately + / - (g / R)* (dt k / 2) 2 and + / -(2g / R)*(dt k / 2) 2 of projection error or, for dt k=4s, the equivalent of 6 and 12 ppm horizontal and vertical accelerometric scale factor error, in rad horizontal attitude error and heading, with g mean Earth gravity 9.81 m / s 2 (at Om), R Average radius of curvature of the Earth 6,400,000 m, or (R / g) 800s.

[0093] Care will be taken not to lose output data at the dt rate k (we choose a cadence much lower than 500s, for example 4s or 10s).

[0094] Furthermore, the second program has the shift values ​​in memory and is arranged to analyze the values ​​of the transmitted processed data and detect the presence of a shift. The analysis consists of comparing each of the components of the most recently received processed data with each of the components of the processed data received the previous instant and detecting an inconsistency therein taking into account the laws of physics. If such an inconsistency exists, this means that a shift has occurred and the second program then considers the ShiftPVdetected indicator as true and compensates for the shift made using the corresponding shift value. Otherwise, the second program considers the ShiftPVdetected indicator as false.

[0095] The second program calculates the evolution of the inertial localization of ti at t2 from the following information:

[0096] - inertial attitude (emitted by the electronic processing circuit 130) at t1 and t2,

[0097] - variation of pseudo-inertial speed in the inertial frame of reference from t1 to t2,

[0098] - duration t2-t1,

[0099] - location at t1.

[0100] As is known in itself, the second program is also designed to exploit:

[0101] - the MC curvature matrix for determining the local curvature of the reference ellipsoid for navigation,

[0102] - the local apparent gravity GravApp (locally perpendicular to the ellipsoid),

[0103] - an external correction factor Corr ext allowing the calculation of apparent gravity to be corrected in order to stabilize the altitude on average on an external altitude reference (in an aircraft, this altitude reference is for example taken from an anemo-barometric unit).

[0104] The second program performs these calculations of the evolution of the inertial localization from ti to t2, taking as hypothesis H1 that the apparent acceleration y P is constant in the navigation frame between ti and t2.

[0105] These calculations are then corrected by taking into account the three correction components of the inertial position from ti to t2 in the inertial frame [i].

[0106] The three components of correction of the inertial position from ti to t2 in the inertial frame [i], CorrPPi (ti -> t2), are calculated as follows:

[0107] - if ShiftPVdetected is false (no speed shift), then

[0108] CorrPPi (t1->t2)= DP (t1->t2)- (PV (t1)

[0109] + PV(t2))*(t1-t2) / 2

[0110] - if ShiftPVdetected is true (there was a speed shift between t1 and t2), then the value of CorrPPi cannot be calculated and is arbitrarily set to 0, i.e.

[0111] CorrPPi (t1->t2)=0

[0112] This calculation is performed by taking as hypothesis H2 that the acceleration f [i] in the inertial frame [i] is constant. The difference between hypotheses H1 and H2 is mainly due to the apparent gravity rotation seen from the navigation frame [p] in the inertial frame [i]. For horizontal mechanized navigation on the terrestrial reference ellipsoid and at free azimuth, this difference has a negligible effect on the calculated position deviation correction term CorrPPi(t1->t2). It is understood that the indicator "SHiftPVdetected" is determined to allow the evaluation of inertial localization error variations to be refined according to the potential dynamics of the carrier at that moment.

[0113] The second program corrects the inertial localization using a CorrPi deviation calculated as follows:

[0114] - projection of the components of CorrPPi(t1->t2) into the navigation frame [p] from the inertial frame [i] which gives the correction components CorrPPp (t1->t2) r using:

[0115] • the inertial attitude emitted by the electronic processing circuit 130 at ti and possibly at t2,

[0116] • the attitude of navigation at t1;

[0117] - calculation of the equivalent rotation correction of the attitude and calculation of the horizontal position on Earth of the horizontal location using the apparent gravity (GravApp) and the MC matrix (2x2) of local curvature of the terrestrial ellipsoid of the navigation in the horizontal navigation reference frame (or platform reference frame) [p] and the two horizontal components of correction CorrPPp (t1->t2);

[0118] - taking this additional rotation into account in the calculations of the evolution of inertial localization from ti to t2;

[0119] - addition of the vertical component of correction CorrPPp (t1->t2) to the altitude at t2 which is the result of the calculation of the evolution of inertial localization from ti to t2 to obtain CorrPi.

[0120] Inertial localization is used here directly to enable navigation of aircraft A.

[0121] In parallel, the second program also receives second signals at t k and is arranged to extract, second signals at t k , the data set of t k-1 to t k , the data set of t k and temporal information and implements a hybrid navigation algorithm to exploit them to calculate a hybrid location (see Figure 6).

[0122] The hybrid navigation algorithm receives as input the location signals at t kand external location data (satellite location data, stellar location data, radar location data, or other).

[0123] The hybrid navigation algorithm includes a known Kalman filter and a hybrid navigation error model to calculate a hybrid location of aircraft A.

[0124] The electronic processing circuit of the inertial measurement unit 100 is arranged to transmit to the electronic navigation calculation unit 200 a time marker (“Time Mark” in FIG. 3) in order to synchronize the navigation calculations and to date the signals transmitted by the inertial measurement unit 100. This is particularly important to enable the hybrid navigation to be dated with respect to the external information that it uses (indeed, it is understood that to calculate a hybrid location at a time t, it is necessary to associate inertial location data and external location data corresponding to said time t).

[0125] The second program corrects the hybridized localization using the correction signals.

[0126] The development of correction signals is now detailed below.

[0127] The electronic processing circuit 100 is provided with a memory containing an error model of the inertial sensors. The electronic processing circuit 100 is arranged to calculate:

[0128] - from the error model, the first ΦUMI correction data which are representative of an impact of sensor errors on the location signals over a given period (for example from t k-1 to t k ) and which are determined by the electronic processing circuit,

[0129] - second QUMI correction data representative of the model noise over the given period.

[0130] More precisely, the first correction data ΦUMI are here the components of an evolution matrix of the nine localization errors in the navigation reference frame [i]. The nine error states correspond to the three states of the attitude errors, to the three states of the pseudo-speed errors and to the three states of the inertial pseudo-position errors. Said matrix may comprise other states representative for example of the impact of the six gyrometric misalignments, of the six accelerometric misalignments, of the scale factor errors of the accelerometers and gyrometers... The calculation of the components of the error evolution matrix is ​​carried out using the error model of the sensors of the inertial measurement unit 100 with measurements of the environment of the inertial measurement unit 100 which are provided by at least one sensor (for example a temperature sensor, a humidity sensor, a magnetic radiation sensor...) arranged in the vicinity of the inertial measurement unit 100 and which are used as input to the error model. It should be noted that the calculation of the components of the error evolution matrix is ​​known in itself and is therefore not detailed here.

[0131] The second QUMI correction data are the components of a vector representing the uncertainties of the error model. This is also referred to as a desensitization matrix or noise matrix, which may or may not be diagonal. Note that the calculation of the components of the model's noise matrix is ​​known in itself and is therefore not detailed here. The first data here are 81 (NxN) and the second data are nine (N).

[0132] The values ​​of the non-zero and non-fixed components of the error evolution matrix and of the three components of the model noise matrix are here coded in 32-bit or 64-bit floating point.

[0133] The electronic processing circuit 100 then puts the first correction data and the second correction data into the form of correction signals.

[0134] It is noted that the electronic processing circuit 100 is here programmed to transmit to the electronic navigation calculation unit 200:

[0135] - on the one hand, at a first rate, location signals and

[0136] - on the other hand, at a second rate lower than the first rate, correction signals for the location signals.

[0137] The second cadence here is a submultiple of the first cadence.

[0138] Note that the given period used for the correction data is sliding from t k-1 to t k , then of t k to t k+1 , then of t k+1 to t k+2 and so on in order to limit the volume of data to be transmitted. It is therefore essential that the electronic navigation calculation unit 200 has all the correction signals.

[0139] It is also important that the content of the location signals at t k and the content of the correction signals are temporally homogeneous in such a way that the data contained in each correction signal corresponds well to the data contained in the location signals corresponding to the given period. There is therefore a synchronization between the development of each correction signal and the development of the location signals during the given period.

[0140] The second program executed by the electronic navigation calculation unit 200 is arranged to extract the first correction data and the second correction data from the correction signals.

[0141] Referring to Figure 6, the second program calculates, by means of a navigation algorithm fed by the location signals at t k and in particular by the batch of location data of t k-1 to t k :

[0142] - the rotation of the measurement frame [m] relative to the inertial frame [i] or I

[0143] - the rotation of the measurement reference [m] relative to the navigation reference [p] is;

[0144] - the rotation speed of the navigation reference [p] relative to the terrestrial reference [t] is;

[0145] - the rotation speed of the terrestrial reference frame [t] relative to the inertial reference frame [i] or .

[0146] With these rotations and rotational speeds, as well as the apparent gravity and the local curvature matrix MC, the second program projects the first correction data ΦuMi(t k-1 to t k) in the navigation frame [p] and thus obtains the first projected correction data Φ NAV (t k-1 to t k ). Using the first projected correction data Φ NAV (t k-1 to t k ), the second correction data QUMi(t k-1 to t k ) and the shift indicator shiftPVdetected of the data set from t0 to t k (obtained by the second program in the same way as for the signaling data at t i ), the second program calculates the error evolutions and the navigation error model which are then transmitted to the hybrid navigation algorithm to recalibrate the hybrid navigation error model, and therefore the hybrid localization, and to the inertial navigation algorithm to also recalibrate the inertial localization.

[0147] The second program provides the inertial localization of aircraft A and the hybrid localization of aircraft A (the localization combines attitude, speed and terrestrial geographic position information).

[0148] It will be noted that, preferably, the electronic navigation unit has a working period of less than half of a minimum time between two successive shifts.

[0149] In the method described, the increments are integrated, by the inertial measurement unit, into an inertial reference frame (apart from sensor defects) so as to allow navigation calculations on a terrestrial reference ellipsoid at a lower rate and asynchronously. The use of the outputs of the inertial measurement unit by the second program, in the case where offsets are possible, is based on the knowledge and use of the pseudo-velocity and pseudo-inertial position offset values ​​upstream of the calculation of the evolution of the inertial location.

[0150] We understand that the transmission of the matrix ΦUMI (t k-1 ->t k ) forming the first correction data for the hybrid navigation(s) allows them to achieve:

[0151] - on the one hand, the calculation of inertial evolution of localization of t k-1 to t kof the first-order linearized inertial measurement unit of the effect of the estimated error parameters, and

[0152] - on the other hand, the calculation of the matrix modeling, also to the first order, the effect of the non-estimated residual errors of the inertial measurement unit on the evolution of the hybrid inertial localization error of t k-1 to t k , before possible recalibrations at t k and after possible adjustments to t k-1 .

[0153] Note that the first-order linearized correction neglects the combined effects of specific force error and gyrometric measurement error between t k-1 and t k on the uncorrected outputs of the inertial measurement unit.

[0154] For durations dt kfrom 1 to a few tens of seconds, depending on the trajectory dynamics of the carrier vehicle, the errors due to this approximation are, for equipment allowing precise pure inertial navigation and for most inertial systems allowing development of attitude and heading functions (AHRS Attitude and Heading Reference Systems) assisted by air speed, negligible compared to the residual errors of non-compensable inertial measurements.

[0155] Taking into account by calculation the parameters of the error model of the inertial measurement unit, estimated by hybrid navigation at t k-1 for the estimated evolution of the hybrid localization uses the first projected correction data Φ NAV (t k-1 ->t k ), the second correction data ΦUMI (t k-1 -»t k ), the values ​​estimated by hybridization and the matrices or quaternion or rotation Tp / t, Tp / m, Tm / i (or Tp / t, Tp / m, Tp / ic , Tm / i and Tm / i c ) to t k-1 state k .

[0156] To facilitate the calculation of <&NAV (which is the error evolution matrix in the navigation frame [p]) from ΦUMI (which is the error evolution matrix in the inertial frame [i]), we have introduced here the compensated inertial frame [i c ] (i.e. the inertial reference frame [i] compensated by taking into account the errors of the inertial measurement unit). Indeed, the reference frame [i] calculated by the QUMI, PVI and PPI outputs (values ​​in m / s and m provided in the reference frame [i]) is not perfect because its calculation is affected by errors of the inertial measurement unit. These errors are modeled in the inertial measurement unit and the quantitative effect of these errors depending on gyrometric and accelerometric error parameters is provided to the hybrid navigation at each step of evolution of t k-1 to t k via the matrixΦUMI (t k-1 -»t k)• The values ​​of some of these parameters are estimated and recalibrated by the Kalman filter, which is also based on the matrix ΦUMI (t k-1 -»t k ) and therefore on the error model that the matrix uses. These values ​​of the error state subvector are used to develop, via the evolution matrix, the angular drift of the reference frame [i] calculated by the inertial measurement unit for hybrid inertial navigation. We therefore have:

[0157] - the three angular error values ​​added to calculate Tp / i corrected at t2 and the average drift between t k-1 and t k to be taken into account to calculate the “projection into [p]” via a matrix M p / i(t k-1 Dt k ) (generally no rotation) for pseudo-velocities and an MM matrix p / i(t k-1 Ot k ) for corrections of pseudo-inertial positions in the [i] frame;

[0158] - the three pseudo-velocity error values ​​in [i] to be added to calculate PVI(t k )-PVI(t k-1 ) corrected for the error parameters estimated at ti by the Kalman filter;

[0159] - the three pseudo-position error values ​​in [i] to, add to calculate PPI(t k-1 )-PPI(t k ) corrected for the estimated error parameters at t k by the Kalman filter.

[0160] This compensation can be used to calculate the evolution of t k-1 to t k of Tp / i also allows to calculate (without this being useful for hybrid navigation) a compensated inertial reference [i c ] which is closer to an inertial reference frame thanks to the corrections of gyrometric errors of parameters estimated and recalibrated by hybrid navigation. It should be noted, however, that the compensated inertial reference frame [i c] is not actually used for navigation calculation. Furthermore, the compensated inertial reference frame [ic] is not necessary to calculate the evolution of t k-1 to t k , of Tp / i, Tp / t, Tp / m, V z , H and Horizontal velocity in the [p] horizontal azimuth reference frame free on the reference ellipsoid.

[0161] We note that:

[0162] - if there are no modeled gyrometric errors (so-called “pure UMI” navigation), then [i] = [i c ],

[0163] - otherwise, the rotation of estimated gyrometric errors of t k-1 to t k in [i c ] is calculated in matrix form for example by *Ti / i c (t k-1 ) where represents the values ​​of the parameter states estimated at t k-1 with Ti c / i * identity matrix and

[0164] The evolutions of the matrices (or quaternions, or vectors representing rotations) Tp / t, Tp / m, and Tp / i c of t k-1 to t k , before possible adjustments to t k , are obtained by iteration of the calculation of rotation evolution from the navigation reference [p] to the reference [i c ] of t k-1 to t k depending on:

[0165] - the average horizontal specific force of the analytical platform of t k-1 to t k ,

[0166] - the correction in average horizontal components in the navigation frame [p] of t k-1 to t k ,

[0167] - the local curvature of the ellipsoid at the mean altitude of t k-1 to t k ,

[0168] - the average vertical speed of t k-1 to t k .

[0169] The curvature generated by the non-spherical reference ellipsoid varies very little and only with latitude and altitude. The curvature matrix can therefore be approximated by a constant (or a linear function with respect to time) over a duration dt k without generating significant errors in calculating the evolution of the location. Thus,

[0170] - a variation in latitude of 5000m (during dt k ) generates a relative variation of the curvatures, at the most unfavorable latitude, of a few ppm at most;

[0171] - an altitude variation of 1000m (in dt k ) generates a relative variation of the curvatures of approximately 1 / 6400, i.e., at 250m / s, a maximum error of approximately 4cm / s. This error is eliminated, except for dynamic phases with vertical acceleration, by using the average altitude on dt k for the calculation of the curvature matrix. The evolution of the vertical velocity of t k-1 to t k, before any adjustments, is obtained by integrating:

[0172] - the average vertical specific force corrected for local gravity estimated at t k-1 ,

[0173] - an apparent gravity correction,

[0174] - a speed stabilization correction,

[0175] - vertical speed errors generated by the estimated UMI errors.

[0176] The evolution of the altitude of t k-1 to t k , is obtained by integration by part of the vertical velocity by adding the correction equal to the vertical component of

[0177] After integration, an external altitude stabilization loop or the reference altitude Kalman filter at t k (e.g. barometric altitude) allows the calculation of the theoretical apparent gravity value at the altitude at t k, the new corrections on the apparent gravity value and possibly the vertical speed at t k applicable for the next time step of t k to t k+1 .

[0178] The consideration of the error model of the inertial measurement unit in the error evolution model of the free-azimuth ellipsoidal hybrid localization uses the matrix ΦUMI t k-1-> t k and the matrices or quaternion or rotation Tp / m, Tp / i, Tm / i at t k-1 state k (values ​​at t k obtained by iteration of the calculation of the evolution of t k-1 to t k). In addition, the error parameter states of the inertial measurement unit are added to the navigation error model. This allows them to be taken into account in the error evolution model of the hybridized localization and possibly the estimation and real-time updating of parameters of the error model of the inertial measurement unit during recalibrations. This is often the case, for example, of accelerometer biases. The method of the invention provides several improvements to facilitate real-time implementation of hybrid navigations with digital links between the inertial measurement unit and the electronic navigation unit.

[0179] These improvements allow the calculation of the evolution of hybridized inertial localization at low rate (rate for example from 1s to 10s depending on the precision desired for the evolution calculation and depending on the dynamic domain of evolution of the carrier).

[0180] The data from this hybrid location has a significant delay (for example 8s) due to:

[0181] • the calculation and transmission times of data by the hybrid integrating inertial measurement unit (for example 4s);

[0182] • to the calculation times for hybrid inertial localization evolution (e.g. 4s);

[0183] • transmission delays (for example 2s) to a high-frequency calculation module (typically 2 to 10ms), and taking into account, by this high-frequency calculation module, low-delay outputs.

[0184] Low delay (typically 4 to 20ms) hybrid navigation operational outputs can be calculated.

[0185] The corresponding navigation calculations are fed:

[0186] • firstly, by low delay and high rate (typically 2 to 10ms) inertial attitude, pseudo-inertial velocity and pseudo-inertial position data,

[0187] • secondly, by the data, at low speed and therefore significantly delayed, from hybrid navigation;

[0188] • and, thirdly, by the time, inertial attitude output, pseudo-inertial velocity and pseudo-inertial position data provided, by the inertial measurement unit, to the iso-dated hybridized inertial navigation.

[0189] It is noted that in the advantageous version of the invention described here, the first program executed by the electronic processing circuit 130 is arranged to carry out a third integration on the first doubly integrated data of the location data of t k-1 to t kto obtain first triply integrated data over the time step considered. The first triply integrated data are transmitted to the electronic processing unit 200 which uses them to refine the navigation. The first triply integrated data of t k-1 to t k serve to improve accuracy.

[0190] Indeed, we initially have pseudo-localization data in the inertial frame [i] while we are trying to obtain navigation in the navigation frame [p].

[0191] We therefore need to calculate the transition matrix from [i] to [p]. To do this, we assume that the specific force f is constant (ramp).

[0192] The transition matrix Ti / p will classically be the sum of matrices composed of the coefficients of the Legendre polynomials.

[0193] With the single integration and double integration of the first data of t k-1 to t k, we can calculate a passage matrix in the form of a first matrix composed of the coefficients of the Legendre polynomials of order 0 and a second matrix composed of the coefficients of the Legendre polynomials of order 1.

[0194] With the third integration of the first data of t k - i to t k , the calculation of the passage matrix Ti / p can be refined by also calculating the coefficients of the Legendre polynomials of order 2 of a third matrix added to the sum of the previous ones. This results in an increase in the precision of the navigation. Of course, the invention is not limited to the embodiment described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0195] In particular, the device may have a structure different from that described.

[0196] For example, the electronic processing circuit and the electronic navigation calculation unit may have structures different from those described and include, for example, a coprocessor, a dedicated ASIC-type processor, a microcontroller, a programmable FPGA-type circuit, etc.

[0197] Although the invention is particularly advantageous when the inertial measurement unit and the electronic processing unit are very far from each other (for example several meters), the invention is also applicable when the inertial measurement unit and the electronic processing unit are closer (for example less than one meter).

[0198] Computer programs can be arranged differently and perform calculations with different accuracies.

[0199] It is noted in particular that the sole provision of correction signals comprising first correction data which are representative of an impact of the errors of the sensors on the location signals over a given period and which are determined by the electronic processing circuit from the error model, and second correction data representative of an effect of the noises and random errors of the inertial measurement unit over the given period, and the exploitation of these correction signals by the navigation calculation unit allows a substantial improvement in the precision. The other characteristics of the embodiment described (such as integration from a single integration start instant or triple integration) are certainly advantageous, but optional.

[0200] Shift operations are not necessary when the integration time is such that the processed data provided will have a value compatible with the resolution expected for navigation.

[0201] The outputs of the electronic processing circuit can be supplied at a fixed rate (possibly configurable via a circuit initialization command) or on external request, with the program making the request then responsible for ensuring a rate of requests sufficient to avoid risking more than a shift of the same data between two supplies.

[0202] Preferably, the attitude outputs (gyrometric data), as well as the velocity outputs and the position outputs (from the accelerometric data) are limited to 22 or 24 bits per output with sufficient resolution to ensure that the degradation of navigation accuracy with the method of the invention is negligible compared to the accuracy of navigation performed directly from the increments from the sensors. The offsets described make it possible to limit the number of bits of the velocity and position outputs.

[0203] The outputs of the electronic processing circuit allow inertial navigation:

[0204] - synchronous or asynchronous,

[0205] - precise even with outputs operating at a rate greater than a few seconds and for a dynamic trajectory,

[0206] - robust to multiple interruptions lasting up to several seconds, and more than a minute in static mode,

[0207] - without overloading the electronic navigation calculation unit in the event of data loss.

[0208] Preferably, the first program executed by the electronic processing circuit has an initialization mode by which all or part of the following parameters can be modified:

[0209] - orientation of the measurement mark,

[0210] - output on demand or on demand,

[0211] - output rate,

[0212] - type of speed output in the inertial frame (note that the output by components in the measurement frame [m] allows the components in the inertial frame to be calculated via the rotation quaternion Qi / m for the transition from [m] to [i] provided),

[0213] - shift thresholds,

[0214] - offset values,

[0215] - bias or scale factor errors...

[0216] Preferably, to minimize the projection error in the navigation reference, navigation with inertial or horizontal mechanization (and navigation reference) with free azimuth on the Earth's ellipsoid will be chosen. However, this is not mandatory.

[0217] Preferably, the effects of variation in gravity, local curvature of the ellipsoid and Coriolis acceleration between times t0 and t are neglected. e .

[0218] In the case where several shifts must be carried out after a single integration, it is necessary to add a shift counter to the data packet so that the electronic calculation unit can find the number of shifts carried out.

[0219] The duration between two shifts can be from a few seconds to a few tens of seconds depending on the dynamics of the vehicle carrying the navigation device. Preferably, to maintain good navigation accuracy, the number of shifts per hour will be limited. For example, with 24-bit coded outputs, the maximum number of shifts is advantageously three per 400s period and, with 32-bit coded outputs, the maximum number of shifts is advantageously three per 28-hour period.

[0220] The device may comprise one or more inertial measurement units arranged in the vicinity of each other (or not), at any point on the aircraft and in particular not necessarily in the vicinity of the center of gravity.

[0221] The integrations are optional if the risk of failure to transmit data between the inertial measurement unit 100 and the electronic navigation calculation unit is sufficiently low to be acceptable with regard to the intended application.

[0222] In a basic navigation version, it is possible to reconstruct the increments at the classic navigation rate from the differences of two successive sets of data output from the inertial measurement unit. Maintenance at this rate of inertial navigation can be carried out in the same way as for classic navigation. In this case, the CorrPPI correction vector is systematically zero.

[0223] The location signals may be developed differently from those described and, for example, correspond only to data integrated from successive integration start times and not from a single integration start time.

[0224] Correction signals can feed one or more hybrid navigation algorithms.

[0225] The first rate can be between 100 Hz and 400 Hz and the second rate can be between 0.1 Hz and 1 Hz: alternatively, they can have different values. The rates can be identical to each other. The respective signal transmission rates can be different from those indicated. As an option regarding the rate, for very high precision use cases with dynamic evolution, one can choose to transmit one to three groups of output values ​​defined below at times distributed over the time interval tl to t2. With a uniform distribution, one obtains a calculation error of evolution due to the rate reduced by four for an additional intermediate data set and reduced by sixteen for three additional intermediate data sets.It is noted that a higher rate of 10s for example generates errors greater than those of a hybridized GNSS navigation: the formula indicated above in the description in fact gives 38 μrad of horizontal projection error. It is greater than the instability of accelerometric scale factors in navigation and the typical residual attitude errors of 30μrad that can be obtained for example by an inertial navigation that is hybridized with a GNSS receiver and that uses an inertial measurement unit sufficiently precise to achieve a typical error of pure inertial horizontal navigation of between one and a few nautical miles per hour.

[0226] The correction data used to recalibrate the hybrid location can come from any source external to inertial navigation, for example the positions of a radiolocation receiver but not only (star sighting or other).

[0227] The worst-case error in calculating the projection of specific forces due to time discretization (t2~ti) is vertically and horizontally with (i)S the Schüler pulsation (about 1 / 840 rad / s ). A time step (t2-ti) of four seconds can sometimes be insufficiently precise for certain applications. Sending Ti / m, PPi and PVi data at intermediate times between tl and t2 (at 1s, i.e. three groups of intermediate Ti / m, PVi and PPi values ​​with t2-tl = 4s for example) allows this error to be sufficiently reduced (by a factor of 16 in the example).

[0228] The invention can be implemented by calculations other than those presented in detail and for example without going through the corrected inertial reference frame.

[0229] The invention is applicable to any type of vehicle, whether land, water or air.

[0230] In the case of hybrid navigation using signals from a Doppler radar or from a vehicle traveling on a predetermined track such as a railway vehicle (the direction of travel is fixed relative to the vehicle platform, defining the reference trihedron [b]), the following are used to calculate the distance traveled as seen from the moving reference point:

[0231] - the simple integral over At of the transition matrix from the frame [i] to the frame of the platform [b] (i.e. nine values);

[0232] - the double integral over At of the transition matrix from the frame [i] to the frame of the platform [b] (i.e. nine values);

[0233] - the triple integral over At of the transition matrix from the frame [i] to the frame of the platform [b] (i.e. nine values);

[0234] - the double integral of the specific force on At (i.e. three values).

[0235] This allows hybridization with models without velocity components transverse to a fixed or quasi-fixed direction relative to the inertial measurement unit.

Claims

CLAIMS 1. Navigation device (1), comprising an inertial measurement unit (100) and an electronic navigation calculation unit (200) connected to each other by a data link (300), the inertial measurement unit (100) comprising inertial sensors (110, 120) for producing location signals and the electronic navigation calculation unit (200) being arranged to calculate a navigation from the location signals, characterized in that the inertial measurement unit (100) comprises an electronic processing circuit (130) connected to the inertial sensors (110, 120) and provided with a memory containing an error model of the inertial measurement unit;in that the electronic processing circuit is arranged to transmit to the electronic navigation unit, on the one hand, at a first rate, said location signals and, on the other hand, at a second rate, correction signals comprising first correction data which are representative of an impact of the errors of the sensors on the location signals over a given period and which are determined by the electronic processing circuit from the error model, and second correction data representative of an effect of the noises and random errors of the inertial measurement unit over the given period;and in that the electronic navigation calculation unit implements a hybrid navigation algorithm arranged to provide a hybrid location which is based on inertial location data extracted from the location signals and the external location data and which is recalibrated from the correction data.; 2. Device according to claim 1, wherein the first correction data are defined in a inertial reference frame and the electronic navigation calculation unit is arranged to use the location signals to project the first correction data into a navigation reference frame.

3. Device according to claim 1 or 2, in which the electronic processing circuit is arranged to emit a time marker with the location signals and the hybrid navigation algorithm uses the time marker to align the inertial location data with the external location data in the hybrid navigation algorithm.

4. Device according to any one of the preceding claims, wherein the second rate is lower than the first rate and, preferably, the second rate is a submultiple of the first rate.

5. Device according to claim 1, in which the electronic processing circuit is arranged to carry out at least a first integration, as a function of time, of primary data contained in primary signals from the inertial sensors over an integration duration, which begins at a single integration start time and which is measured, to produce processed data inserted into signals forming the location signals with time information representative of the integration duration, and in that the electronic navigation calculation unit (200) is arranged to extract the processed data and the time information from the location signals and use them to calculate the navigation taking into account the integration duration.

6. Device according to claim 5, in which the electronic processing circuit (130) is arranged to carry out a second integration on the result of the first integration of at least part of the primary data, the processed data comprising the result of the first integration and the result of the second integration.

7. Device according to claim 6 or 7, in which the electronic processing circuit (130) is arranged to compare at least part of the integrated data with at least a first threshold and to, when the integrated data has a current value at least equal to the first threshold, apply to the integrated data a first predetermined offset to bring the integrated data back to a value offset below the first threshold.

8. Device according to claim 5, in which the electronic processing circuit (130) is arranged to carry out two successive integrations on at least part of the data and, when the doubly integrated data has a current value exceeding a second threshold, apply to the doubly integrated data a second predetermined shift to bring the doubly integrated data back to a shifted value below the second threshold.

9. Device according to claim 8, in which the electronic navigation calculation unit (200) is arranged for each reception of data from the inertial measurement unit (100): . acquire an inertial attitude at the instant of the current reception and memorize that of the previous reception, . reconstruct, between two receptions, a variation of pseudo-inertial speed in the inertial frame, corrected for the effect of the first shifts, . calculate, from an evolution of the position in the inertial frame corrected for the effect of the second shifts, a term compensating for the fact that the acceleration (f[ij) in the inertial frame is not constant over the time separating two receptions; calculate a time evolution between the current reception and the previous reception.

10. Device according to claim 5, in which the electronic processing circuit (130) is arranged to: perform at least a first integration of at least part of the primary data, a second integration on the result of the first integration, and a third integration on the result of the second integration; calculate, from the results of the first integration and the results of the second integration, a transition matrix from the inertial reference frame to the navigation reference frame in the form of a first matrix composed of the coefficients of the Legendre polynomials of order 0 and a second matrix composed of the coefficients of the Legendre polynomials of order 1; calculate, from the result of the third integration, the coefficients of the Legendre polynomials of order 2 of a third matrix added to the sum of the previous ones to refine the calculation of the transition matrix.

11. Method of navigation by means of a navigation device (1) comprising an inertial measurement unit (100) and an electronic navigation calculation unit (200) connected to each other by a data link (300), comprising the steps of - in the inertial measurement unit (100): . developing location signals from measurements of inertial sensors (110, 120) and transmitting the location signals to the navigation computing electronics unit at a first rate, from an error model of the inertial sensors recorded in the inertial measurement unit, developing correction signals comprising first correction data which are representative of an impact of the sensor errors on the location signals over a given period, and second correction data representative of the evolution noises representative of the model errors over the given period, and transmitting the correction signals to the navigation computing electronics unit at a second rate; and - in the electronic navigation calculation unit (200): by means of a hybrid navigation algorithm, calculating a hybrid location which is based on inertial location data extracted from the location signals and external location data, . recalibrate the hybrid localization from the correction data.

12. Vehicle containing at least one device according to any one of claims 1 to 10.

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