Navigation device and method using data pre-integrated asynchronously 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) interconnected by a data link (300), the inertial measurement unit (100) comprising inertial sensors (110, 120) providing first signals containing first data representing a speed variation and second data representing an angle variation, and the electronic navigation computation unit (200) being arranged to compute a navigation from signals provided by the inertial measurement unit (100), characterised in that the inertial measurement unit (100) includes an electronic processing circuit (130) connected to the inertial sensors (110, 120) and arranged to perform at least one first integration, as a function of time, of the first data and the second data over an integration time, which starts at a single integration start time and is measured, in order to produce first processed data and second processed data contained in second signals with time information representing the integration time, and in that the electronic navigation computation unit (200) is arranged to extract, from the second signals, the processed data and the time information and utilise them to compute the navigation, taking into account the integration time separating two consecutive extractions.

Description

[0001] NAVIGATION DEVICE AND METHOD USING DATA PRE-INTEGRATED ASYNCHRONOUSLY 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 Figure 6 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. The inertial measurement unit 1100 comprises accelerometers and angular sensors arranged along the axes of a measurement frame [m] to provide signals representative of the integral, over a time step (between an instant t i-1 and a moment 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 t1, then from instant t1 to an instant t2, then from instant t2 to an instant t3, etc.: the signals are therefore generally called increments.

[0005] Specific force (in English "specific force", "g-force" or "mass-specific force") is a representation of the sum of the acceleration relative to the inertial frame and the Earth's gravity.

[0006] 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 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 frequency, 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.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] However, in aircraft, it is envisaged to group the computers, including the electronic calculation unit of the navigation system, in one or more avionics bays located at the same point of the aircraft. The inertial measurement unit should preferably be located as close as possible to the center of gravity of the aircraft. However, in such a case, the inertial measurement unit would be connected to the electronic calculation unit, located in the avionics bay, by an Ethernet link, for example, compliant with the ARINC664 standard.

[0008] However, any disruption in signal transmission, for example due to lightning, could lead to a loss of data and would therefore be detrimental to navigation accuracy.

[0009] To mitigate this risk, a fiber optic connection could be used, although this is relatively expensive. Alternatively, a specific data exchange protocol could be used, with data transmission redundancy to ensure that no data is lost. However, this results in an overloaded connection and an increase in computing load.

[0010] OBJECT OF THE INVENTION The invention aims in particular to overcome at least in part the aforementioned drawbacks.

[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 providing first signals containing first data representative of variations in linear speeds and second data representative of variations in angular attitudes. The electronic navigation calculation unit is arranged to calculate a navigation from signals provided by the inertial measurement unit.According to the invention, the inertial measurement unit comprises an electronic processing circuit connected to the inertial sensors and arranged to carry out at least a first integration, as a function of time, of the first data and the second data over an integration duration, measured from a single integration start instant, to produce first processed data and second processed data contained in second signals with time information representative of the integration duration. The electronic calculation unit is arranged to extract the processed data and the time information from the second signals and use them to calculate the navigation taking into account the integration duration separating two successive extractions.

[0013] Thus, it is no longer the first signals (the increments produced by the inertial sensors) which are transmitted at high frequency to the electronic navigation calculation unit as in the prior art, but values ​​integrated over an unbounded integration duration from the single initialization instant (the same for all the first data, corresponding for example to the start-up of the system or to the reception of a start-of-integration command), which can be transmitted at the same frequency or at a lower frequency. It is understood that the second signals successively sent by the electronic processing circuit will be representative of an integration from instant t0 to an instant t1, then from instant t0 to an instant t2, then from instant t0 to an instant t3, etc.In this way, whatever the instant at which a second signal is received, it is representative of an integration from the single instant of start of integration, i.e. t0 in the previous example. This transmission is less restrictive and the risk of transmission error is limited. The processing of the data to form the second signals which will be transmitted therefore makes the transmission of the data and the navigation calculation carried out from said data more reliable. Such a transmission is advantageous at short distance but also at relatively long distances (several meters).

[0014] According to a particular characteristic of the invention, the electronic processing circuit is arranged to compare the first integrated data with at least a first threshold and, when the first integrated data has a current value exceeding the first threshold, to apply to the first integrated data a predetermined offset to bring the first integrated data back to a value offset below the first threshold.

[0015] Preferably, the electronic processing circuit is arranged to carry out two successive integrations on the first data and, when the first doubly integrated data has a current value exceeding a second threshold, apply to the first doubly integrated data a second predetermined shift to bring the first doubly integrated data back to a shifted value below the second threshold.

[0016] Then, according to a particular mode of implementation, the electronic navigation calculation unit is arranged to, upon each reception of data from the inertial measurement unit:

[0017] . acquire the inertial attitude at the instant of the current reception and memorize that of the previous reception,

[0018] . reconstruct the variation, between two receptions, of pseudo-inertial speed in the inertial frame corrected for the effect of the first shifts,

[0019] . calculate, from the evolution of the position in the inertial frame corrected for the effect of the second offsets, a term compensating for the fact that the acceleration 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.

[0020] Preferably then, the electronic navigation calculation unit is arranged to, upon each reception of data from the inertial measurement unit: calculate the evolution of the location since the last reception from:

[0021] . of the inertial attitude of the current reception, of the inertial attitude of the previous reception, of the variation of pseudo speed, of the term compensating for the fact that the acceleration in the inertial frame is not constant over the time separating two receptions and of the evolution of time; . of the last calculated location;

[0022] - and via a navigation algorithm, assuming that the apparent acceleration is constant in the navigation reference frame over the time separating two receptions, to provide a location grouping together information on attitude, speed and terrestrial geographic position.

[0023] 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. The method comprises the steps of

[0024] - in the inertial measurement unit:

[0025] . measuring a variation in linear speeds and a variation in angular attitude by means of inertial sensors providing first signals containing first data representative of the variation in linear speeds and second data representative of the variation in angular attitude, carrying out processing comprising at least a first integration of the first data and the second data over an integration duration from a single integration instant, producing first processed data and second processed data contained in second signals with time information representative of the integration duration; and

[0026] - in the electronic calculation unit:

[0027] . extract the processed data and time information from the second signals,

[0028] . use them to calculate navigation taking into account the integration time between two successive extractions.

[0029] The invention finally relates to a vehicle equipped with a navigation device according to the invention. Other characteristics and advantages of the invention will emerge on reading the following description of a particular and non-limiting embodiment of the invention.

[0030] BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Reference will be made to the attached drawings, including:

[0032] [Fig. 1] Figure 1 is a partial schematic view of an aircraft equipped with a navigation device according to the invention;

[0033] [Fig. 2] Figure 2 is a schematic view of the device according to the invention;

[0034] [Fig. 3] Figure 3 is a flowchart showing the data exchanges during the implementation of the method according to the invention;

[0035] [Fig. 4] Figure 4 is a flowchart showing the implementation of the method according to the invention, on the inertial measurement unit side;

[0036] [Fig. 5] Figure 5 is a flowchart showing the implementation of the method according to the invention, on the electronic calculation unit side;

[0037] [Fig. 6] Figure 6 is a flowchart showing the data exchanges in a navigation device according to the prior art.

[0038] DETAILED DESCRIPTION OF THE INVENTION

[0039] 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.

[0040] 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.

[0041] 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 relative to the previous measurement. The inertial reference frame [i] is, for example, the measurement reference frame when the inertial measurement unit 100 is switched on or any other inertial reference frame angularly offset from the latter.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 reference frame [m]. The rotation increments are thus representative of the variation of the integral over time of the angular rotation speed of the measurement reference frame [m] with respect to the inertial reference frame [i] and are provided in the form of quaternions, Euler angles, rotation matrices, or Bortz vectors. The inertial sensors thus provide first signals containing first data representative of a variation in gravitational speed (accelerometric measurement) and second data representative of a variation in angles (gyrometric measurement). Conventionally, these signals are provided at a rate of between 100 Hz and 400 Hz.

[0042] 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 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.

[0043] 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 inertial navigation from the signals supplied by the inertial measurement unit 100. This second program will also be detailed later. The inertial measurement unit 100 and the electronic navigation calculation unit 200 each have a clock allowing the former to date the signals transmitted and the latter to date the times of reception.

[0044] 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 the data link 300. The data link 300 is here an Ethernet link for example compliant with the ARINC664 standard.

[0045] The first program executed by the electronic processing circuit 130 receives as input the first signals containing the first data and the second data. It is arranged to carry out:

[0046] - a first integration, over an integration duration measured from a single instant of start of integration t0 (the integration duration is noted t e - in figures 3 and 4), second data to produce second integrated data;

[0047] - a projection of the first data into the inertial frame [i] to obtain first projected data;

[0048] - 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;

[0049] - a first shift (Shift V) 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);

[0050] - a second integration of the first processed data, over the integration duration measured from the single integration start time t0, to produce first doubly integrated data;

[0051] - a second shift (Shift P) 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).

[0052] The first program executed by the electronic processing circuit is arranged to calculate the floating or fixed point integrations with a number of mantissa bits making it possible to achieve the required localization precision with a minimum time between two successive shifts of 20 s. A double precision calculation on 64 bits including 48 mantissa bits makes it possible to achieve a precision objective of, for example, 0.001 m.s. -1 , 0.001 m, 0.001 ° / h and 1 μrad.

[0053] We understand that:

[0054] - the second integrated data are representative of an angular position (or an orientation);

[0055] - the first integrated data and the first processed data are representative of a linear speed;

[0056] - the first doubly integrated data and the first doubly processed data are representative of a linear position.

[0057] The first shift operation comprises the step of comparing an absolute current 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 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 SVitesse ) is deduced from the current 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 ​​[ -Svitesse ; +Svitesse ] . The first threshold Svitesse 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 .

[0058] 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 first 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 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 Sposition threshold) is deduced from the current value of the first doubly integrated data (or added according to the sign of the current 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 Sposition threshold is determined according to an expected position resolution for navigation. The integration time without offset depends on the dynamics of the aircraft A and the SPosition threshold. The first doubly integrated data and the second SHP offset value are expressed here in meters.

[0059] 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), 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), 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 transmitted via the data link 300 to the electronic navigation calculation unit 200.

[0060] The second program executed by the electronic navigation calculation unit 200 is arranged to extract the processed data and the time information from the second signals and to use them to calculate the navigation taking into account the evolution of the integration time since the last extraction of the second signals.

[0061] More precisely, with reference to Figure 5, the second program receives as input the second signals, in the form of two data packets, emitted at each instant t eby the first program but recovered respectively for example at time ts1 then at time t2, each comprising the first processed data, the first doubly processed data, the second processed data, and 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.

[0062] Considering for the simplicity of the description that the data received at time t1 have already been used, the second program must carry out the operations allowing calculation from the data received at time t2:

[0063] - the three components of variation of the pseudo-inertial velocity from t1 to t2 in the measurement frame [m], noted DVm(t1-> t2), corrected for the effect of an SHV shift;

[0064] - the three components of variation of the pseudo-inertial velocity from t1 to t2 in the inertial frame [i], noted DVi(t1-> t2), corrected for the effect of an SHV shift;

[0065] - the three components of variation of the pseudo-inertial position from t1 to t2 in the inertial frame [i], noted DP(t1->t2), corrected for the effect of an SHP shift;

[0066] - the three components of correction of the pseudo-inertial position from t1 to t2 in the inertial frame [ i ], noted CorrPPi ( t1->t2),

[0067] - a logic indicator Shif tPVdetected for detecting a shift in at least one of the pseudo-speed components between t1 and t2•

[0068] We recall that the data received at time t1 and the data received at time t2 have been integrated since the start time of integration t0. It is therefore sufficient to subtract the data received at time t1 from those received at time t2 to obtain the data corresponding to the time interval t2-t1.

[0069] Furthermore, the second program has the shift values ​​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 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 possible dynamics of the vehicle and the laws of physics. If such an inconsistency exists, this means that a shift has occurred and the second program then considers the indicator ShiftPVdetected as true and compensates for the shift made using the corresponding shift value. Otherwise, the second program considers the indicator ShiftPVdetected as false.

[0070] The second program calculates the evolution of the inertial localization from t1 to t2 from the following information:

[0071] - inertial attitude (emitted by the electronic processing circuit 130) at t1 and t2,

[0072] - variation of pseudo-inertial speed in the inertial frame of reference from t1 to t2,

[0073] - of duration t2- t1,

[0074] - location at t1.

[0075] In a manner known in itself, the second program is also arranged to exploit:

[0076] - the MC curvature matrix for determining the local curvature of the reference ellipsoid for navigation relative to the Earth,

[0077] - the local apparent gravity GravApp (locally perpendicular to the ellipsoid),

[0078] - an external correction factor Corr ext allowing the calculation of apparent gravity to be corrected by stabilizing the altitude.

[0079] The second program performs these calculations of the evolution of the inertial localization from t1 to t2 taking as hypothesis H1 that the apparent acceleration Υ p is constant in the navigation frame between t1 and t2.

[0080] These calculations are then corrected by taking into account the three correction components of the inertial position from t1 to t2 in the inertial frame [i].

[0081] The three components of correction of the inertial position from t1 to t2 in the inertial frame [i], CorrPPi (t1-> t2), are calculated as follows:

[0082] - if ShiftPVdetected is false (no speed shift), then

[0083] CorrPPi (t1->t2) = DP (t1->t2) - (PV (t1)

[0084] + PV(t2) ) * ( t1-t2) / 2

[0085] - 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.

[0086] CorrPPi (t1->t2) =0

[0087] This calculation is carried out 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 with free azimuth, this difference has a negligible effect on the calculated position deviation correction term CorrPPi ( t1-> t2). It is understood that the indicator "SHif tPVdetected" 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.

[0088] The second program corrects the inertial localization using a CorrPi deviation calculated as follows:

[0089] - 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), using:

[0090] • the inertial attitude emitted by the electronic processing circuit 130 at t1 and possibly at t2,

[0091] • the attitude of navigation at t1;

[0092] - 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 frame [p] and the two horizontal components of correction CorrPPp (t1->t2);

[0093] - taking into account this additional rotation in the calculations of the evolution of inertial localization from t1 to t2;

[0094] - 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 t1 to t2 to obtain CorrPi.

[0095] This corrected data is then used by the second program via a navigation algorithm, known in itself, to provide the location of aircraft A (the location groups together information on attitude, speed and terrestrial geographic position).

[0096] 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.

[0097] The present invention relates to the integration of these increments, by the inertial measurement unit, into an inertial reference frame (apart from sensor defects) so as to enable navigation calculations on a terrestrial reference ellipsoid at a lower frequency 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.

[0098] 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.

[0099] In particular, the device may have a structure different from that described.

[0100] 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.

[0101] 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). The second distance is not limited by the first distance: the second distance can be less, greater, or equal to the first distance depending on the needs and the configuration of the vehicle. The computer programs can be arranged differently and perform the calculations with different accuracies.

[0102] 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.

[0103] 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, it being up to the program making the request to ensure a rate of requests sufficient to not risk more than a shift of the same data between two supplies.

[0104] Preferably, the attitude outputs (gyrometric data), as well as the speed 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 speed and position outputs.

[0105] The outputs of the electronic processing circuit allow inertial navigation:

[0106] - synchronous or asynchronous,

[0107] - precise even with exploitation of outputs at a rate greater than a few seconds and for a dynamic trajectory,

[0108] - robust to multiple interruptions that can last up to several seconds, and more than a minute in static mode, - without overloading the electronic navigation calculation unit in the event of data loss.

[0109] 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:

[0110] - orientation of the measurement mark,

[0111] - output on demand or on demand,

[0112] - output rate,

[0113] - type of speed output (in the measurement frame or in the inertial frame),

[0114] - shift thresholds,

[0115] - offset values,

[0116] - bias or scale factor errors...

[0117] 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. This is not, however, obligatory.

[0118] Preferably, the effects of variation of gravity, local curvature of the ellipsoid and Coriolis acceleration between times t0 and t are neglected. e .

[0119] 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.

[0120] 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.

[0121] 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.

[0122] In a basic version of navigation, 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 correction vector CorrPPi is systematically zero.

[0123] The invention is applicable to any type of vehicle, whether land, water or air.

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) providing first signals containing first data representative of a speed variation and second data representative of an angle variation, and the electronic navigation calculation unit (200) being arranged to calculate a navigation from signals provided by the inertial measurement unit (100), characterized in that the inertial measurement unit (100) comprises an electronic processing circuit (130) connected to the inertial sensors (110, 120) and arranged to perform at least a first integration, as a function of time, of the first data and the second data over a period integration, which begins at a single instant of start of integration and which is measured,to produce first processed data and second processed data contained in second signals with time information representative of the integration time, and in that the electronic navigation calculation unit (200) is arranged to extract from the second signals the processed data and the time information and to use them to calculate the navigation taking into account the integration time separating two successive extractions., 2. Device according to claim 1, in which the electronic processing circuit (130) is arranged to perform a second integration on the result of the first integration of the first data, the processed data comprising the result of the first integration and the result of the second integration.

3. Device according to any one of the preceding claims, in which the electronic processing circuit (130) is arranged to compare the first integrated data with at least a first threshold and, when the first integrated data has a current value exceeding the first threshold, to apply to the first integrated data a first predetermined offset to bring the first integrated data back to a value offset below the first threshold.

4. Device according to claim 3, in which the electronic processing circuit (130) is arranged to carry out two successive integrations on the first data and, when the first doubly integrated data has a current value exceeding a second threshold, apply to the first doubly integrated data a second predetermined shift to bring the first doubly integrated data back to a shifted value below the second threshold.

5. Device according to claim 4, in which the electronic navigation calculation unit (200) is arranged to, upon each reception of the data from the inertial measurement unit (100): acquire the inertial attitude at the instant of the current reception and memorize that of the previous reception, reconstruct the variation, between two receptions, of pseudo-inertial speed in the inertial reference frame, corrected for the effect of the first offsets, . calculate, from the evolution of the position in the inertial frame corrected for the effect of the second offsets, a term compensating for the fact that the acceleration (f[i]) in the inertial frame [i] is not constant over the time separating two receptions; calculate a time evolution between the current reception and the previous reception.

6. Device according to claim 5, in which the electronic navigation calculation unit (200) is arranged to, upon each reception of data from the inertial measurement unit (100): calculate the evolution of the location since the last reception from: . of the inertial attitude of the current reception, of the inertial attitude of the previous reception, of the variation of pseudo speed, of the term compensating for the fact that the acceleration (f [i]) in the inertial frame [i] is not constant over the time separating two receptions and of the evolution of time; . of the last calculated location; - and via a navigation algorithm, known in itself, assuming that the apparent acceleration is constant in the navigation reference frame over the time separating two receptions, to provide a location grouping together information on attitude, speed and terrestrial geographic position.

7. Device according to any one of claims 4 to 6, in which the first threshold and the second threshold are determined as a function of an expected resolution for navigation.

8. Device according to any one of claims 3 to 7, in which the electronic navigation unit has a working period less than half of a minimum time between two successive shifts.

9. Device according to any one of the preceding claims, in which the electronic processing circuit (130) is arranged to emit the second signals at the request of the electronic navigation calculation unit.

10. Device according to any one of claims 1 to 8, in which the electronic processing circuit (130) is arranged to emit the second signals to predetermined time intervals.

11. Device according to any one of the preceding claims, in which the electronic processing circuit (130) is arranged to calculate the floating point integrations in double precision on 64 bits including 48 mantissa bits.

12. Device according to any one of the preceding claims, in which the inertial measurement unit (100) and the electronic navigation calculation unit (200) are in two separate housings and the data link (300) is of the Ethernet type.

13. 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): . measuring an accelerometric variation and a gyrometric variation by means of inertial sensors (110, 120) providing first signals containing first data representative of an accelerometric variation and second data representative of a gyrometric variation, . carry out processing comprising at least a first integration of the first data and the second data over a predetermined integration period, . produce second signals comprising the first processed data and the second processed data and time information; and in the electronic navigation calculation unit (200): . extract the processed data and time information from the second signals, use them to calculate navigation taking into account the integration time.

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

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