Method and device for aligning the inertial navigation of a vehicle.

Abstract

The invention relates to an inertial navigation alignment device for a vehicle, comprising: - an inertial navigation system (INS1) intended to be installed in the vehicle, equipped with a first target (MIR1); - a reference inertial navigation system (INS_REF) equipped with a reference target (MIR_REF) having a higher accuracy than the first system and adapted to measure the direction of the Earth's axis of rotation; - an alignment arm (BRA) equipped with cameras (CAM1, CAM_REF) at its ends, said arm being configured to be installed partly inside the vehicle and partly outside the vehicle, with the targets in the field of view of the cameras; - a processing unit (UC) connected to the inertial measurement units and the cameras to align the navigation of the first system (INS1) with the navigation of the reference system (INS_REF). Figure 1 (for the abstract)

Description

Title of the invention: Method and device for inertial navigation alignment of a vehicle. Technical field of the invention

[0001] The present invention relates to the field of inertial navigation of a vehicle, in particular for a space launcher. Technological background

[0002] During its launch, a space launcher must have an on-board navigation solution for its piloting and / or localization.

[0003] For this purpose, an inertial navigation system is generally used, which includes in particular an inertial navigation unit (this unit includes accelerometers and gyroscopes).

[0004] Indeed, the inertial navigation system must integrate information on the attitude of the launcher during its mission (the effective horizontality and the azimuth heading which gives the orientation with respect to geographic North).

[0005] The inertial navigation system must be initialized on the launch pad of the launcher while it is stationary. This improves the navigation accuracy calculated by the system during the mission.

[0006] The phase during which the inertial navigation system is initialized is called the alignment phase. The inertial navigation system must be sufficiently precise to measure the Earth's rotation in order to deduce the azimuth heading for the launcher and to measure the direction of gravity in order to deduce the horizontality (or verticality) of the system.

[0007] This requires an inertial navigation system with sufficient accuracy to measure the direction of the Earth's axis of rotation: 360° in 24h or approximately 0.004° / s), which is therefore capable of performing autonomous alignment and is consequently expensive.

[0008] In the current context where we see the emergence of low-cost launchers (micro-launchers), it is necessary to reduce the cost of an inertial navigation system and therefore to use less precise systems (particularly with regard to gyroscopes) which no longer allow autonomous alignment.

[0009] It is therefore necessary to perform a heading insertion in the inertial navigation system.

[0010] To this end, various techniques exist, such as estimating the heading based on the environment. However, heading estimation can quickly become subject to significant error.

[0011] Beyond space launchers, similar problems can be encountered for other types of vehicles when that vehicle needs to know its static alignment.

[0012] One objective of the invention is to provide a method for performing inertial navigation alignment that does not present at least one of the aforementioned drawbacks. Summary of the invention

[0013] To this end, an inertial navigation alignment device for a vehicle is proposed, the device comprising: - a first inertial navigation system intended to be carried in the vehicle, said first system being equipped, on one of its external faces, with a first target; - a second inertial navigation system, called the reference system, having on the one hand a greater accuracy than the first inertial navigation system and adapted on the other hand to measure the direction of the Earth's axis of rotation, said reference inertial navigation system being equipped, on one of its external faces, with a target called the reference target; - an alignment arm equipped with a first camera at one end and a second camera at the other end, said alignment arm being configured so that it can be installed by placing the first target in the field of vision of a first camera and placing the reference target in the field of vision of a second camera; and - a computing unit connected to the first inertial navigation system, the reference inertial navigation system and the cameras so that said computing unit can align the navigation of the first inertial navigation system with the navigation of the reference inertial navigation system.

[0014] The invention also relates to a method for aligning the inertial navigation of a vehicle implemented with a device according to the invention, said method comprising the following steps: a) place one end of the alignment arm equipped with the first camera inside the vehicle so that the first target of the first inertial navigation system is in the field of vision of the first camera; b) position the reference inertial navigation system so that the reference target is in the field of vision of the second camera; c) connect the first inertial navigation system, the reference inertial navigation system and the cameras to the computing unit; d) perform an autonomous alignment of the reference inertial navigation system; e) align the inertial navigation of the first inertial navigation system with the inertial navigation provided by the reference inertial navigation system.

[0015] Thus, thanks to the device and the method according to the invention, it is possible to perform an alignment of the inertial navigation, without the disadvantages of known techniques, and at a reduced cost.

[0016] The process according to the invention may comprise one or more of the steps below, taken individually or in combination with each other: - Step e) includes the following sub-steps: ej measure a distance and angular offsets between the first target of the first inertial navigation system and the first camera; e2) measure a distance and angular offsets between the reference target of the reference inertial navigation system and the second camera; e3) from the information obtained in substeps ej and e2), deduce a distance and angular offsets between the first inertial navigation system and the reference inertial navigation system; then e4) insert the inertial navigation data from the reference inertial navigation system into the first inertial navigation system, by compensating for the distance and angular offsets determined in substep e3); - during step e), we also define an uncertainty rate of the inertial navigation alignment of the first inertial navigation system.

[0017] The invention also relates to a method for calibrating a device according to the invention, comprising the following steps: A) measure a distance and angular offsets between the first target and gyroscopes of the first inertial navigation system; B) measure a distance and angular offsets between the reference target and gyroscopes of the reference inertial navigation system; C) measure a distance and angular offsets between the two cameras located at the respective ends of the alignment arm (BRA).

[0018] The calibration process may further include the following steps: any one of step A) or step B) is carried out on a marble slab comprising a marble target and positioning means for an inertial navigation system whose position relative to the marble target is known, the process comprising the following substeps: - install the inertial navigation system equipped with its target on the marble positioning means, the gyroscopes of the inertial navigation system then presenting a known position relative to the positioning means; - position a camera so that the marble target and the inertial navigation system target are in the camera's field of vision; - provide a computing unit and connect it to the inertial navigation system and the camera; - determine, using the calculation unit, a distance and angular offsets between the marble target and the target of the inertial navigation system; - determine, using the calculation unit, a distance and angular offsets between the target of the inertial navigation system and the gyroscopes of the inertial navigation system knowing a position of the positioning means relative to a position of the marble target, a position of the gyroscopes of the inertial navigation system relative to the positioning means and, a distance and angular offsets between the marble target and the target of the inertial navigation system.

[0019] Finally, during calibration, step c) may be carried out on a marble (MRB*) comprising a first target whose position on the marble is known and a second target whose position on the marble is also known, said method comprising the following sub-steps: - place the alignment arm equipped with its cameras on a support placed on the marble, positioning the first target in the field of vision of the first camera and the second target in the field of vision of the second camera; - provide a computing unit and connect it to the two cameras; - determine, using the calculation unit, a distance and angular offsets between each camera and the target that is in its field of vision, then - determine, using the calculation unit, a distance and angular offsets between the two cameras. Brief description of the figures

[0020] The invention will be better understood with the aid of the following description, given solely by way of example and made with reference to the accompanying drawings in which: - [Fig.1] represents an inertial navigation alignment device of a vehicle according to the invention; - The [Fig.2] is a diagram representing the main steps of an inertial navigation alignment process of a vehicle, implemented with the device of the [Fig.1]; - Fig. 3 is a diagram representing the main steps of a calibration process; - Figure 4 represents a calibration installation that can be used to implement certain steps in the calibration process.

[0021] - Figure 5 represents another installation that can be used to put implementing other steps of the calibration process. Detailed description of the invention

[0022] The invention proposes an inertial navigation alignment device D for an HCV.

[0023] Reference may be made to [Fig. 1].

[0024] The inertial navigation alignment device D of an HCV includes: - a first inertial navigation system INS1 intended to be carried in the vehicle, said first system being equipped, on one of its external faces, with a first target MIR1; - a second inertial navigation system INS_REF, called the reference system, which can for example be installed outside the vehicle, having a precision which is on the one hand greater than that of the first inertial navigation system INS1 and on the other hand adapted to measure the direction of the Earth's axis of rotation, said reference inertial navigation system being equipped, on one of its external faces, with a reference target MIR_REF; - an alignment arm BRA equipped with a first camera CAM1 at one end and a second camera CAM_REF at the other end, said alignment arm being configured so that it can be installed by placing the first target MIR1 in the field of view of the first camera CAM1 and placing the reference target MIR_REF in the field of view of the second camera CAM_REF; and - a computing unit UC connected to the first inertial measurement unit INS1, to the reference inertial measurement unit INS_REF and to the cameras CAM1, CAM_REF so that said computing unit can align the navigation of the first inertial navigation system INS1 with the reference inertial navigation system INS_REF.

[0025] To pass the arm inside the vehicle, for example a space launcher as illustrated in [Fig. 1], an existing TRH manhole in the launcher's fuselage must be used. This is generally an access hatch to equipment allowing a part of a worker's body to pass through.

[0026] An inertial navigation system typically includes accelerometers and gyroscopes. The difference between the first inertial navigation system INS1 and the reference inertial navigation system INS_REF lies at least in the accuracy provided by the gyroscopes. The accuracy of the gyroscopes in the first inertial navigation system INS1 does not allow for autonomous alignment, unlike the reference inertial navigation system INS_REF.

[0027] With such a device D, an inertial navigation alignment method for a vehicle can be implemented, the main steps of which are schematically shown in [Fig.2].

[0028] The inertial navigation alignment method comprises the following steps: a) placing one end of the alignment arm BRA equipped with the first camera CAM1 inside the VHC vehicle so that the first target MIR1 of the first inertial navigation system INS1 is in the field of view of the first camera; b) positioning the reference inertial navigation system INS_REF so that the reference target MIR_REF is in the field of view of the second camera CAM_REF; c) connect the first inertial navigation system INS1, the reference inertial navigation system INS_REF and the cameras CAM1, CAM_REF to the computing unit UC; d) perform an autonomous alignment of the INS_REF reference inertial navigation system; e) align the inertial navigation of the first inertial navigation system INS1 using the inertial navigation provided by the reference inertial navigation system INS_REF.

[0029] More particularly, step e) may include the following substeps: e0 measure the distance and angular offsets between the first target MIR1 of the first inertial navigation system INS1 and the first camera CAM1; e2) measure the distance and angular offsets between the reference target MIR_REF of the reference inertial navigation system INS_REF and the second camera CAM_REF; e3) from the information obtained in substeps ej and e2), deduce the distance and angular offsets between the first inertial navigation system INS1 and the reference inertial navigation system INS_REF; then e4) insert the inertial navigation of the reference inertial navigation system INS_REF into the first inertial navigation system INS1, by compensating for the distance and angular offsets determined in substep e3).

[0030] The implementation of steps ej to e4) is carried out with pre-calibrated devices (CAM1 and CAM_REF cameras, the BRA arm, and also the INS1 and INS_REF inertial navigation systems). In particular, with regard to each of the inertial navigation systems, the compensation between the target and the gyroscopes of an inertial navigation system is already integrated by means of a prior calibration of the device. This calibration is discussed later.

[0031] Furthermore, during step e), one can also define an uncertainty rate of the inertial navigation alignment of the first inertial navigation system INS1 with respect to the inertial navigation provided by the reference inertial navigation system INS_REF.

[0032] Before implementing the method according to the invention, for example on a launch pad for a space launcher, calibration of various elements is necessary.

[0033] Indeed, while the alignment device and method described above allow, during their implementation, the determination of a distance and angular offsets between a camera and a target within its field of view, the quality of the alignment requires calibration between the gyroscopes of each inertial navigation system and the target carried by said system, as well as prior calibration of the BRA alignment arm. This ensures that the measurements taken will indeed allow alignment (with a known and controlled risk of error) of the navigation of the first inertial navigation system INS1 with respect to that of the reference inertial navigation system INS_REF.

[0034] In the following, we therefore describe the different calibrations implemented before the device according to the invention can be used.

[0035] To calibrate the device D of the invention, the following main steps should be carried out: A) measure distances and angular offsets between the first target MIR1 and the gyroscopes of the first inertial navigation system INS1; B) measure distances and angular offsets between the reference target MIR_REF and the gyroscopes of the reference inertial navigation system INS_REF; C) measure distances and angular offsets between the two cameras CAM1, and CAM_REF located at the respective ends of the BRA alignment arm.

[0036] Reference may be made to [Fig.3].

[0037] To implement step A) of the calibration process, an MRB marble shown in [Fig.4] can be used.

[0038] The MRB marble comprises a target MIR_MRB and positioning means M_POS for an inertial navigation system (in this case we have represented on [Fig.4] the first inertial navigation system INS1 for step A). ​​The position of the positioning means M_POS relative to the target of the marble MIR_MRB is known.

[0039] Step A) of the process may include the following substeps: - install the INS1 inertial navigation system equipped with its MIR1 target on the M_POS positioning means of the marble, the gyroscopes of the system inertial navigation INS1 then presents a known position relative to the positioning means; - position a CAM_MRB camera so that the target of the marble MIR_MRB and the target MIR1 of the inertial navigation system INS1 are in the field of vision of the camera; - provide a computing unit UC and connect it to the INS1 inertial navigation system and the CAM_MRB camera; - determine, using the calculation unit UC, the distance and angular offsets between the MIR_MRB target of the marble and the MIR1 target of the INS1 inertial navigation system; - determine, using the computing unit UC, the distance and angular offsets between the MIR1 target of the INS1 inertial navigation system and the gyroscopes of the INS1 inertial navigation system.

[0040] Step A) according to these substeps can be carried out provided that the following are known: i) the position of the positioning means M_POS relative to the target on the marble slab MIR_MRB, ii) the position of the gyroscopes of the inertial measurement system relative to the positioning means M_POS. The distance and angular offsets between the target MIR_MRB on the marble slab and the target MIR1 of the inertial navigation system are determined during calibration.

[0041] Step B) of the calibration process can be carried out using sub-steps identical to those described above for step A). ​​The reference inertial navigation system INS_REF is then subjected to the same calibration steps as the first inertial navigation system.

[0042] As for step C) of the calibration process, it can be carried out on an MRB* marble comprising a first target MIR*1 whose position on the marble is known and a second target MIR*2 whose position on the marble is also known.

[0043] Reference may be made to [Fig.5].

[0044] Step C) may therefore include the following sub-steps: - place the BRA alignment arm equipped with its CAM1, CAM_REF cameras on an SPT support placed on the MRB* marble by placing the first target MIR*1 in the field of vision of the first CAM1 camera and the second target MIR*2 in the field of vision of the second CAM_REF camera; - Provide a computing unit (CU) and connect it to the two cameras CAM1 and CAM_REF; - Determine, using the computing unit (CU), the distance and angular offsets between each camera and the target that is in its field of view, then - determine, using the computing unit UC, the distance and angular offsets between the two cameras CAM1, CAM_REF.

[0045] Step C) according to these sub-steps can be carried out insofar as the position of the target of the marble MIR*1 is known in relation to the target of the marble MIR*2.

Claims

Demands

1. Inertial navigation alignment device (D) for a vehicle, the device comprising: - a first inertial navigation system (INS1) intended to be carried in the vehicle, said first system being provided, on one of its external faces, with a first target (MIR1); - a second inertial navigation system (INS_REF), referred to as the reference system, having on the one hand a greater accuracy than that of the first inertial navigation system (INS1) and adapted on the other hand to measure the direction of the Earth's axis of rotation, said reference inertial navigation system being provided, on one of its external faces, with a target referred to as the reference system (MIR_REF);- an alignment arm (BRA) equipped with a first camera (CAM1) at one end and a second camera (CAM_REF) at the other end, said alignment arm being configured so that it can be installed by placing the first target (MIR1) in the field of view of a first camera (CAM1) and by placing the reference target (MIR_REF) in the field of view of a second camera (CAM_REF); and - a computing unit (UC) connected to the first inertial navigation system (INS1), the reference inertial navigation system (INS_REF) and the cameras (CAM1, CAM_REF) so that said computing unit can align the navigation of the first inertial navigation system (INS1) with respect to the navigation of the reference inertial navigation system (INS_REF).

2. A method for aligning the inertial navigation system of a vehicle implemented with a device according to claim 1, said method comprising the following steps: a. placing one end of the alignment arm (BRA) equipped with the first camera (CAM1) inside the vehicle such that the first target (MIR1) of the first system inertial navigation (INS1) either in the field of vision of the first camera (CAM1); b. position the reference inertial navigation system (INS_REF) so that the reference target (MIR_REF) is in the field of vision of the second camera (CAM_REF); c. connect the first inertial navigation system (INS1), the reference inertial navigation system (INS_REF) and the cameras (CAM1, CAM_REF) to the computing unit (CU); d. perform an autonomous alignment of the inertial reference navigation system (INS_REF); e. align the inertial navigation of the first inertial navigation system (INS1) using the inertial navigation provided by the reference inertial navigation system (INS_REF).

3. A method according to the preceding claim, wherein step e) comprises the following substeps: ei) measure a distance and angular offsets between the first target (MIR1) of the first inertial navigation system (INS1) and the first camera (CAM1); e2) measure a distance and angular offsets between the reference target (MIR_REF) of the reference inertial navigation system (INS_REF) and the second camera (CAM_REF); e3) from the information obtained in substeps ei) and e2), deduce a distance and angular offsets between the first inertial navigation system (INS1) and the reference inertial navigation system (INS_REF); then e4) insert the inertial navigation data from the reference inertial navigation system (INS_REF) into the first inertial navigation system (INS1), by compensating for the distance and angular offsets determined in substep e3).

4. A method according to any one of claims 2 or 3, wherein in step e) an uncertainty rate of the inertial navigation alignment of the first inertial navigation system (INS1) is also defined.

5.

6. A method for calibrating a device according to claim 1, comprising the following steps: A. measure a distance and angular offsets between the first target (MIR1) and gyroscopes of the first inertial navigation system (INS1); B. measure a distance and angular offsets between the reference target (MIR_REF) and gyroscopes of the reference inertial navigation system (INS_REF); C. measure a distance and angular offsets between the two cameras (CAM1, CAM_REF) located at the respective ends of the alignment arm (BRA). A calibration method according to the preceding claim, wherein any one of step A) or step B) is carried out on a marble (MRB) comprising a target (MIR_MRB) of the marble and positioning means (M_POS) for an inertial navigation system (INS1, INS_REF) whose position relative to the target of the marble is known, the method comprising the following substeps: - install the inertial navigation system (INS1, INS_REF) equipped with its target (MIR1, MIR_REF) on the positioning means (M_POS) of the marble (MRB), the gyroscopes of the inertial navigation system then presenting a known position relative to the positioning means; - position a camera so that the marble target (MIR_MRB) and the inertial navigation system target (MIR1, MIR_REF) are in the camera's field of vision; - provide a computing unit (CU) and connect it to the inertial navigation system and the camera; - determine, using the calculation unit (CU), a distance and angular offsets between the target (MIR_MRB) of the marble and the target (MIR1, MIR_REF) of the inertial navigation system; - determine, using the computing unit (CU), a distance and angular offsets between the target (MIR1, MIR_REF) of the inertial navigation system (INS1,

7. INS_REF) and the gyroscopes of the inertial navigation system knowing a position of the positioning means (M_POS) relative to a position of the marble target, a position of the gyroscopes of the inertial navigation system relative to the positioning means and, a distance and angular offsets between the marble target (MIR_MRB) and the target (MIR1, MIR_REF) of the inertial navigation system. Calibration method according to claim 5 or 6, wherein step c) is carried out on a marble (MRB*) comprising a first target (MIR*1) whose position on the marble is known and a second target (MIR*2) whose position on the marble is also known, said method comprising the following substeps: - place the alignment arm (BRA) equipped with its cameras (CAM1, CAM_REF) on a support (SPT) placed on the marble (MRB*) by placing the first target (MIR*1) in the field of vision of the first camera (CAM1) and the second target (MIR*2) in the field of vision of the second camera (CAM_REF); - provide a computing unit (CU) and connect it to the two cameras; - determine, using the computing unit (CU), a distance and angular offsets between each camera and the target that is in its field of vision, then - determine, using the computing unit (CU), a distance and angular offsets between the two cameras (CAM1, CAM_REF).

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