Inertial core for inertial measurement unit and associated inertial measurement unit

Abstract

Inertial Core for Inertial Measurement Unit and Associated Inertial Measurement Unit. The present invention relates to an inertial core (10) of an inertial measurement unit comprising an inertial sensor set (12) including at least one accelerometer (16) and at least one gyroscope (18), wherein a first sensor (12) of the sensor set (12) defines at least one mounting surface (20). At least one second sensor (12) of the sensor set (12) is fixed to said first sensor (12) at said mounting surface (20), the first sensor (12) forming a mounting structure for said second sensor (12). Figure for the abstract: Figure 2

Description

Title of the invention: Inertial core for inertial measurement unit and associated inertial measurement unit

[0001] The present invention relates to the field of inertial measurements and more particularly, but not exclusively, to inertial navigation.

[0002] The present invention relates in particular to inertial cores for inertial measurement units and to associated inertial measurement units.

[0003] This applies particularly to inertial systems whose purpose is to determine the location and navigation of a moving object, for example, an aircraft. These systems comprise at least one inertial measurement unit, as well as a set of external sensors producing instantaneous measurements characterizing the location and / or navigation of said moving object. One application of such a system is, for example, aircraft navigation.

[0004] In a known manner, an inertial measurement unit commonly designated "IMU" according to the acronym corresponding to the English terminology "Inertial Measurement Unit", comprises an inertial core, also designated "ISA" for "Inertial Sensors Assembly", formed of several inertial sensors which deliver one or more measurements describing the movement of the mobile.

[0005] In a typical use case, the inertial sensors are gyroscopes and / or accelerometers, commonly three of each type, arranged along three orthogonal axes.

[0006] Each accelerometer delivers an acceleration signal representative of the acceleration undergone by the inertial core it equips, along a given axis (linked to this inertial core).

[0007] Each gyroscope delivers an angular velocity signal, representative of an angular velocity of rotation of the inertial core it equips around a given axis (linked to this inertial core).

[0008] Said sensors are conventionally carried by a rigid mechanical structure, which is itself mounted in the mobile.

[0009] Navigation calculations performed on the elementary data measured by the inertial sensors require preliminary processing consisting of expressing the output quantities of the different sensors in a single orthogonal coordinate system. To do this, compensations for axis misalignment are made to account for machining defects during the mounting of the sensors on the rigid mechanical structure.

[0010] Said axis alignment defects are usually compensated as a function of temperature with a model that may give rise to modeling errors. These modeling errors are all the smaller when the initial axis alignment errors are small and have low temperature sensitivity.

[0011] One way to reduce these axis misalignment errors is therefore to mount the sensors on a mechanical structure with the highest possible rigidity. Such a mechanical structure is, for example, made of steel or aluminum alloy. However, some errors may still occur.

[0012] One aim of the invention is therefore to provide an inertial core allowing better control of axis alignments.

[0013] To this end, the invention relates to an inertial core of an inertial measurement unit comprising a set of inertial sensors including at least one accelerometer and at least one gyroscope, in which a first sensor of the set of sensors defines at least one reception surface, at least a second sensor of the set of sensors being fixed to said first sensor at the level of said reception surface, the first sensor forming a reception structure for said second sensor.

[0014] Fixing several sensors together makes it possible to reduce the number of axis transfers, and therefore to improve the control and stability of axis alignments.

[0015] According to other advantageous aspects of the invention, the inertial core comprises one or more of the following features, taken individually or in all technically possible combinations:

[0016] - all sensors in the sensor set other than the first sensor are fixed audit first sensor at the level of a reception surface of said first sensor, said first sensor forming a reception structure for said sensors;

[0017] - the first sensor comprises a monolithic block, the second sensor(s) being fixed to said monolithic block;

[0018] - the monolithic block comprises at least one cavity, the second sensor(s) being received at least in part in the said cavity or cavities;

[0019] - the monolithic block is made of a material exhibiting thermal expansion less than 10 ppm / °C, preferably 5 ppm / °C;

[0020] - the monolithic block is made of a glass-ceramic material;

[0021] - the first sensor is a tri-axial gyroscope forming a housing structure for three single-axis accelerometers;

[0022] - the second sensor(s) are attached to the first sensor by gluing, welding or by means of mechanical fixings;

[0023] - the inertial core being devoid of an intermediate mechanical structure additional intended to serve as a support for the sensors.

[0024] The invention also relates to an inertial measuring unit comprising an inertial core of the aforementioned type and a signal processing unit from the inertial sensors.

[0025] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0026] [Fig-1] [Fig.1] is a schematic representation of an inertial measurement unit according to the invention, comprising an inertial core; and

[0027] [Fig.2] [Fig.2] is a perspective view of the inertial core of [Fig.1].

[0028] Fig. 1 schematically represents an embodiment of an inertial measuring unit 8 according to the present invention.

[0029] The inertial measurement unit 8 is configured to be carried on board a mobile, for example an aircraft, and is suitable for providing navigation measurements of said mobile.

[0030] The inertial measuring unit 8 is advantageously rigidly linked to the moving part, for example to a structural element of the moving part, either directly or by means of a support.

[0031] The inertial unit 8 comprises an inertial core 10 including a set 11 of inertial sensors 12, and a signal processing unit 14 from the inertial sensors 12.

[0032] Fig. 2 represents an inertial core 10 according to an embodiment of the invention.

[0033] The set 11 of inertial sensors 12 comprises at least one accelerometer 16 and at least one gyroscope 18. Each sensor 12 is configured to deliver an inertial signal representative of an acceleration or angular velocity of rotation of the inertial measurement unit 8.

[0034] Each accelerometer 16 delivers an acceleration signal representative of the acceleration undergone by the inertial measuring unit 8 with which it is equipped, along one or more orthogonal axes of a first orthogonal frame given (linked to the inertial measuring unit 8).

[0035] Each gyroscope 18 delivers an angular velocity signal, representative of an angular velocity of rotation of the inertial measurement unit 8 that it equips around one or more orthogonal axes of a second orthogonal frame given (linked to the inertial measurement unit 8).

[0036] Said acceleration and angular velocity signals constitute inertial signals, providing information on the dynamics of the inertial measurement unit 8.

[0037] The acceleration and angular velocity signals delivered by the accelerometers and gyroscopes equipping the inertial core 10 make it possible to fully determine the three components of the acceleration vector of the inertial measuring unit 8 comprising said inertial core 10, as well as the three components of the angular velocity vector of this measuring unit 8.

[0038] The sensors 12 are selected from single-axis, dual-axis and tri-axis sensors. This means that said sensors are capable of measuring an acceleration or an angular velocity along one, two or three axes respectively.

[0039] For example, as in the embodiment shown in [Fig.2], the inertial core 10 includes a tri-axial gyroscope 18 and three mono-axial accelerometers 16 (only two accelerometers are visible).

[0040] Alternatively, the inertial core 10 comprises three single-axis gyroscopes 18 or one single-axis gyroscope and one bi-axial gyroscope.

[0041] Alternatively or in addition, the inertial core 10 includes a mono-axial accelerometer 16 and a bi-axial accelerometer 16, or a tri-axial accelerometer 16.

[0042] A first sensor 12 of the set 11 of sensors 12 is configured to form a host structure for at least one second sensor 12 of the sensor set. The first sensor 12 is subsequently designated as the host sensor and each subsequent second sensor 12 is subsequently designated as the received sensor.

[0043] The receiving sensor 12 is typically larger than the received sensor(s).

[0044] Preferably, the inertial core 10 includes a host sensor 12 configured to form a host structure for all sensors 12 other than said host sensor 12, of the inertial core 10.

[0045] Advantageously, the inertial core 10 is devoid of an additional mechanical support for the sensors 12, so that the receiving sensor 12 serves as a receiving structure for all the other sensors 12. In other words, the receiving sensor 12 plays the role of a rigid mechanical support.

[0046] The receiving sensor 12 has at least one receiving surface 20 intended to receive at least one second sensor 12 from the set of sensors 12. Each received sensor 12 is fixed to the receiving sensor 12 at the level of a receiving surface 20.

[0047] The received sensor(s) 12 are, for example, attached to the receiving sensor 12 by gluing, welding, or by means of mechanical fasteners.

[0048] In the embodiment of [Fig. 2], the inertial core 10 comprises a tri-axial gyroscope 18 and three mono-axial accelerometers 16, only two of which are visible. The gyroscope 18 acts here as the first sensor, or receiving sensor, and the accelerometers 16 act as second sensors, or receiving sensors.

[0049] Thus, the gyroscope 18 has a plurality of reception surfaces 20 on which the accelerometers 16 are fixed.

[0050] Preferably, the first sensor 12 comprises a monolithic block 22 to which the second sensor(s) are attached. The monolithic block 22 thus acts as a support for the second sensor(s) 12.

[0051] Advantageously, the monolithic block 22 includes at least one receiving cavity 24, the second sensor(s) 12 being received at least in part in said cavity(es) 24.

[0052] For example, in the embodiment shown in [Fig. 2], the gyroscope 18 is a tri-axial laser gyroscope, comprising a monolithic block 22 in which three optical paths are cut, arranged orthogonally in pairs, and six mirrors 26 (four of which are visible in [Fig. 2]) connected in pairs by the optical paths. WO 2009 / 101105 describes an example of a tri-axial laser gyroscope.

[0053] In the case of the embodiment of [Fig. 2], the monolithic block 22 has the general shape of a cube with cut corners. However, the monolithic block 22 is capable of having other shapes.

[0054] The monolithic block 22 has three receiving cavities 24, each cavity 24 being delimited by internal walls 25 and being intended to receive at least in part a given accelerometer 16.

[0055] The said cavities 24 are here provided between the optical paths.

[0056] The accelerometers 16 are received in said cavities 24 and fixed at the level of said internal walls 25.

[0057] The arrangement of sensors 12 in cavities 24 facilitates the alignment of said sensors 12 and improves their accuracy. It is indeed possible to automate the creation of said cavities in order to adjust the surfaces intended to receive the second sensors 12.

[0058] This also makes it possible to reduce the size of the inertial core 10, by nesting the sensors 12 forming said core together.

[0059] Preferably, as shown in [Fig.2], the receiving sensor 12 has a symmetrical structure and the received sensors 12 are positioned symmetrically on the receiving sensor 12, which improves the control of axis alignments.

[0060] According to an advantageous embodiment shown in [Fig. 2], the monolithic block 22 also has one or more additional cavities 28, which are not intended to receive sensors. These additional cavities 28 make it possible to reduce the mass of the inertial core 10.

[0061] Preferably, the monolithic block 22 is made of a material having a thermal expansion of less than 10 ppm / °C, preferably 5 ppm / °C. Having low thermal expansion thus allows greater stability over time of the alignment axes of the inertial core 10. In particular, this makes it possible to avoid or at least reduce the deviation of the axes of the second sensors 12 with respect to the receiving sensor 12.

[0062] For example, the monolithic block 22 is made of a glass-ceramic material.

[0063] The processing unit 14 includes an electronic processing circuit connected to the inertial sensors 12 and is adapted to retrieve the signals from the sensors 12 and process them by implementing at least one localization algorithm (more commonly called an inertial navigation algorithm) which is configured to calculate real-time information on the position (latitude, longitude, altitude), speed and attitude (heading, roll and pitch angles of the inertial core) of the inertial core 10 under consideration. Such a unit 14 is known in itself.

[0064] By eliminating the intermediate mechanical structure, the inertial core 10 according to the invention makes it possible to remove an axis transfer and thus improve the accuracy and stability of the axis alignment. Each second sensor 12 is directly transferred to the receiving sensor 12, or even directly integrated into it, taking advantage of the available space in the receiving sensor 12. This eliminates the need for two transfers (accelerometers on the intermediate part and gyroscope on the same intermediate part), leaving only one to be considered.

[0065] In addition, the transfer of the received sensor(s) 12 onto the receiving sensor 12 is capable of being automated, further improving the accuracy of axis alignment, as well as the repeatability of operations.

[0066] The inertial core 10 according to the invention also takes advantage of the non-functional surfaces and spaces of the receiving sensor 12 to accommodate the received sensor(s) 12, which significantly reduces its compactness compared to an inertial core comprising an intermediate mechanical structure. This compactness is accompanied by an increase in the frequencies of the inertial core's natural modes, thus avoiding interactions that are normally difficult to handle.

[0067] The removal of the intermediate mechanical structure also allows a reduction in the mass of the inertial core 10, as well as a reduction in costs.

[0068] Variations are possible.

[0069] For example, according to one variant, the host sensor 12 is a triaxial accelerometer 16 forming a host structure for gyroscopes 18.

[0070] According to one embodiment, the host sensor 12 is a single-axis or dual-axis sensor, forming a host structure for all the other sensors. For example, the host sensor 12 is a single-axis laser gyroscope or a single-axis fiber gyroscope.

Claims

Demands

1. Inertial core (10) of an inertial measuring unit (8) comprising an array (11) of inertial sensors (12) including at least one accelerometer (16) and at least one gyroscope (18), wherein a first sensor (12) of the array (11) of sensors (12) defines at least one receiving surface (20), at least a second sensor (12) of the array (11) of sensors (12) being fixed to said first sensor (12) at the level of said receiving surface (20), the first sensor (12) forming a receiving structure for said second sensor (12).

2. Inertial core (10) according to claim 1, wherein all the sensors (12) of the set (11) of sensors (12) other than the first sensor (12) are fixed to said first sensor (12) at the level of a surface (20) for hosting said first sensor (12), said first sensor (12) forming a structure for hosting said sensors (12).

3. Inertial core (10) according to claim 1 or 2, wherein the first sensor (12) comprises a monolithic block (22), the second sensor(s) (12) being fixed to said monolithic block (22).

4. Inertial core (10) according to claim 3, wherein the monolithic block (22) comprises at least one cavity (24), the second sensor(s) (12) being received at least in part in said cavity(s) (24).

5. Inertial core (10) according to claim 3 or 4, wherein the monolithic block (22) is made of a material having a thermal expansion of less than 10 ppm / °C, preferably 5 ppm / °C.

6. Inertial core (10) according to any one of claims 3 to 5, wherein the monolithic block (22) is made of a glass-ceramic material.

7. Inertial core (10) according to any one of the preceding claims, wherein the first sensor (12) is a tri-axial gyroscope (18) forming a host structure for three mono-axial accelerometers (16).

8. Inertial core (10) according to any one of the preceding claims, wherein the second sensor(s) (12) are attached to the first sensor (12) by gluing, welding or by means of mechanical fasteners.

9. Inertial core (10) according to any one of the preceding claims, said inertial core (10) being devoid of a structure

10. additional intermediate mechanical system intended to serve as a support for the sensors (12). Inertial unit (8) comprising • an inertial core (10) according to any one of the preceding claims; and • a signal processing unit (14) from inertial sensors (12).

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