Vibration-resistant gyrometer

Abstract

A gyrometer including a first dual-mass gyrometer including a planar substrate, first left and right inertial masses including a first left and right frames, respectively, aligned along a first excitation axis X.sub.1 parallel to an excitation direction, and mounted with the ability to slide on the substrate along the first excitation axis X.sub.1, and first left and right central masses, respectively, mounted with the ability to slide in the first left and right frames, respectively, parallel to a first detection direction perpendicular to the excitation direction; a first coupling spring interposed between the first left and right frames; a first rocker mounted with the ability to rotate on the substrate about a first rocker pivot, first left and right ends of the first rocker being connected to the first left and right central masses, respectively; second left and right inertial masses aligned along a second axis X.sub.2 parallel to the excitation direction, and mounted with the ability to slide on the substrate along the second axis X.sub.2.

Claims

1. A gyrometer comprising: 1) a first dual-mass gyrometer comprising a planar substrate extending in a plane, first left and right inertial masses comprising: first left and right frames, respectively, aligned along a first excitation axis X.sub.1 parallel to an excitation direction, and mounted with the ability to slide on the substrate along said first excitation axis X.sub.1, and first left and right central masses, respectively, mounted with the ability to slide in the first left and right frames, respectively, parallel to a first detection direction perpendicular to the excitation direction; a first oscillation-inducing actuator inducing oscillation, in the excitation direction, of the first left and right inertial masses and of a first coupling spring; a first rocker mounted with the ability to rotate on the substrate about a first rocker pivot, first left and right ends of the first rocker being connected to the first left and right central masses, respectively; and a first detector of the angular position of the first rocker about the first rocker pivot; 2) second left and right inertial masses aligned along a second axis X.sub.2 parallel to said excitation direction, and mounted with the ability to slide on the substrate along the second axis; the gyrometer further comprising left and right arms, mounted with the ability to rotate on the substrate about a left arm pivot and a right arm pivot, respectively, having axes perpendicular to the substrate, the left arm mechanically coupling the first left frame with the second left inertial mass, and the right arm mechanically coupling the first right frame with the second right inertial mass; the first coupling spring being interposed between said first left and right frames and/or a second coupling spring being interposed between said second left and right inertial masses.

2. The gyrometer according to claim 1, comprising the said second coupling spring.

3. The gyrometer according to claim 2, comprising a second dual-mass gyrometer comprising: said second left and right inertial masses, said second left and right inertial masses comprising: second left and right frames, respectively, aligned along the second axis known as “second excitation axis” X.sub.2, and mounted with the ability to slide on the substrate along the second excitation axis X.sub.2, and second left and right central masses, respectively, mounted with the ability to slide in the second left and right frames, respectively, parallel to a second detection direction, identical to or different than the first detection direction; said second coupling spring, interposed between said second left and right frames; a second oscillation-inducing actuator inducing oscillation, in the excitation direction, of the second left and right inertial masses and of the second coupling spring, the second actuator being identical to or different than the first actuator; a second rocker mounted with the ability to rotate on the substrate about a second rocker pivot, second left and right ends of the second rocker being connected to the second left and right central masses respectively; and a second detector of the angular position of the second rocker about the second rocker pivot.

4. The gyrometer according to claim 3, wherein the second left and right inertial masses, the second coupling spring, the second oscillation-inducing actuator, the second rocker, and the second detector of the angular position are respectively identical to the first left and right inertial masses, the first coupling spring, the first oscillation-inducing actuator, the first rocker, and the first detector of the angular position; and/or the left and right arms are identical.

5. The gyrometer according to claim 3, wherein the left arm is mounted with the ability to rotate on the first and second left frames, about first and second left axes of rotation which are perpendicular to the excitation direction, respectively, and/or the right arm is mounted with the ability to rotate on the first and second right frames, about first and second right axes of rotation which are perpendicular to the excitation direction, respectively.

6. The gyrometer according to claim 3, comprising a control module comprising a phase-locked loop circuit configured to control the first and second actuators.

7. The gyrometer according to claim 3, wherein the first and second detection directions are identical, the first detector is configured to provide a first measurement of a rotation of the first rocker about the first rocker pivot, the second detector is configured to provide a second measurement of a rotation of the second rocker about the second rocker pivot, the gyrometer comprising a module configured to provide a signal on the basis of the first and second measurements.

8. The gyrometer according to claim 1, wherein the first detection direction is parallel to the plane of the first excitation axis and of the second axis, and to the plane in which the substrate extends.

9. The gyrometer according to claim 1, wherein the first left inertial mass is mechanically coupled to the second left inertial mass exclusively with the left arm, and the first right inertial mass is mechanically coupled to the second right inertial mass exclusively with the right arm.

10. The gyrometer according to claim 1, wherein said first detector comprises a piezoresistive strain gage or a capacitive gauge.

11. The gyrometer according to claim 10, wherein said gauge comprises at least one nanowire connecting the first rocker and to the substrate, the distance between a point of mechanical connection of said nanowire to the first rocker and said first rocker pivot being less than 100 microns, or connecting at least one of the left and right arms to the substrate.

12. The gyrometer according to claim 1, wherein the left and right arms are shaped in such a way that the resonant frequency at which the assembly of the first and second left inertial masses oscillates, in the excitation direction, in phase-opposition with the assembly of the first and second right inertial masses is different than any one of the resonant frequencies of the first central masses, in the first detection direction.

13. The gyrometer according to claim 12, wherein said difference is greater than 1 kHz.

14. The gyrometer according to claim 13, wherein the position of the left arm pivot along the left arm is configured in such a way that the moments of force exerted by gravity, oriented in the excitation direction, on the left arm by the first and second left inertial masses about the left arm pivot compensate one another.

15. The gyrometer according to claim 1, wherein the left arm and/or the right arm has/have: a length greater than 100 microns and less than 2000 microns; and/or a width greater than 10 microns and less than 50 microns, and/or an aspect ratio equal to the ratio length/width greater than 5 and less than 30.

16. The gyrometer according to claim 1, wherein each of the second left and right inertial masses is a monobloc mass.

17. The gyrometer according to claim 1, comprising a plurality of assemblies each comprising one respective set of said second left and right inertial masses, aligned along a respective so-called second axis, parallel to said excitation direction, and mounted with the ability to slide on the substrate along said respective second axis; and for each said assembly, respective left and right arms, mounted with the ability to rotate on the substrate about left arm and right arm pivots respectively, having axes perpendicular to the substrate, for each said assembly, the left arm mechanically coupling the first left frame to the respective second left inertial mass, and the right arm mechanically coupling the first right frame to the respective second right inertial mass.

18. The gyrometer according to claim 17, wherein, for each said assembly, each of the second left and right inertial masses is a monobloc mass.

19. A method of using a gyrometer according to claim 1, said method comprising subjecting said gyrometer to external vibrations at a frequency of 40 kHz under 10 g.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and advantages of the invention will become more apparent from reading the detailed description which follows and from studying the attached drawing, given solely for illustrative purposes, in which:

(2) FIG. 1 schematically depicts, in a view from above, a dual-mass gyrometer;

(3) FIG. 2 illustrates the normal operation of the gyrometer of FIG. 1 when the substrate is rotating about an axis of rotation oriented in the direction Z;

(4) FIG. 3 illustrates unbalanced operation of the gyrometer of FIG. 1 when it is rotating about an axis of rotation oriented in the direction Z;

(5) FIGS. 4 to 7 schematically depict, in a view from above, a gyrometer according to the invention actuated according to the 4 main mechanical excitation modes;

(6) FIGS. 8 and 9 schematically depict, viewed from above and face-on, a variant of a dual-mass gyrometer, FIG. 9 only partially depicting the gyrometer of FIG. 8;

(7) FIG. 10 schematically depicts, in a view from above, a “two-axis” gyrometer according to the invention;

(8) FIG. 11 illustrates the positioning of the arm pivots

(9) FIG. 12 schematically depicts, in a view from above, a gyrometer according to the invention in an embodiment in which the second inertial masses are monobloc masses;

(10) FIG. 13 schematically depicts, in a view from above, a gyrometer according to the invention in an embodiment in which the gyrometer comprises several sets of monobloc left and right inertial masses;

(11) FIG. 14 schematically depicts, in a view from above, a gyrometer according to the invention in an embodiment in which the second inertial masses are monobloc masses coupled by a coupling spring;

(12) FIG. 15 schematically depicts, in a view from above, a gyrometer according to the invention in an embodiment in which the gyrometer comprises several sets of monobloc left and right inertial masses coupled by a respective coupling spring.

(13) For the sake of clarity, the first and second dual-mass gyrometers of a gyrometer according to the invention have been depicted only partially.

(14) In the various figures, identical references are used to denote components that are identical or analogous.

DETAILED DESCRIPTION

(15) As FIGS. 1 to 3 were described in the preamble, reference is made now to FIG. 4.

(16) A gyrometer according to the invention comprises first and second dual-mass gyrometers 5.sub.1 and 5.sub.2 respectively, which are either identical or different. First and second dual-mass gyrometers that are different are advantageous for achieving a “two-axis” gyrometer.

(17) Single-Axis Gyrometer

(18) A single-axis gyrometer is able only to measure speeds of rotation about axes of rotation that are parallel to a predefined direction.

(19) FIGS. 1 to 7 relate to a single-axis gyrometer which is able to measure speeds of rotation only about axes of rotation that are parallel to the direction Z.

(20) The dual-mass gyrometers 5.sub.1 and 5.sub.2 are similar to the one described in the preamble. Unless indicated otherwise, the dual-mass gyrometer description of the preamble therefore applies to each of the first and second dual-mass gyrometers of a gyrometer according to the invention.

(21) For the sake of clarity, the same references are used for each of the dual-mass gyrometers, the references of the first and second dual mass gyrometers being assigned a suffix “1” or “2” respectively, however. The components are also designated in the same way, the designations of components of the first and second dual-mass gyrometers however being qualified as “first” or “second”, respectively.

(22) As depicted in FIG. 4, the first and second dual-mass gyrometers 5.sub.1 and 5.sub.2 are placed on a planar common substrate 10, side by side, along first and second excitation axes X.sub.1 and X.sub.2 which are parallel. The first and second dual-mass gyrometers 5.sub.1 and 5.sub.2 are arranged top to tail, the first left and right frames facing the second left and right frames, respectively. In other words, the first and second rockers 20.sub.1 and 20.sub.2 face toward the outside of the gyrometer.

(23) Alternatively, the first and second dual-mass gyrometers 5.sub.1 and 5.sub.2 may be oriented toward one another, the first and second rockers 20.sub.1 and 20.sub.2 facing one another and the second left and right frames opening onto the inside of the gyrometer.

(24) According to the invention, the gyrometer comprises left 30g and right 30d arms, the left arm mechanically coupling the first left inertial mass 12.sub.g1 to the second left inertial mass 12.sub.g2, and the right arm mechanically coupling the first right inertial mass 12.sub.d1 to the second right inertial mass 12.sub.d2.

(25) The left and right arms are preferably identical. They are preferably coupled in the same way to the inertial masses they connect. Only the left arm and its arrangement are therefore described hereinafter, this description also applying to the right arm.

(26) The left arm comprises first and second ends which are mounted with the ability to rotate on the first and second left frames 12.sub.g1′ and 12.sub.g2′ respectively, about prong pivots 33.sub.g1 and 33.sub.g2, respectively, parallel to the direction Z. A mounting with the ability to rotate may be obtained, for example, by a local reduction in the amount of material or by a local modification to the nature of the material of the prong.

(27) As a preference, the left arm comprises a left rod 32g and two left prongs 34.sub.g1 and 34.sub.g2 which are connected to the first and second left frames 12.sub.g1′ and 12.sub.g2′ respectively.

(28) The two left prongs project from the left rod, in the manner of a fork. The left arm thus has the overall shape of a very flattened U.

(29) The prong pivots 33.sub.g1 and 33.sub.g2 are preferably the result of a localized reduction of the material of the left prongs 34.sub.g1 and 34.sub.g2, in the excitation direction X. Advantageously, such a local reduction in material also gives a transverse stiffness, in the detection direction Y, that is lower than the stiffness in the excitation direction X.

(30) The left rod 32g is mounted with the ability to rotate about a left arm pivot 35g rigidly secured to the substrate 10 and oriented perpendicular to the substrate. As a preference, the left arm pivot 35g allows only rotation about an axis perpendicular to the plane of the substrate.

(31) The torsional stiffness about the left arm pivot is low.

(32) The contribution of mechanical stiffness for the inertial masses along the excitation axis needs to be negligible in comparison with the stiffness of the guide springs 16.

(33) This pivot connection to the substrate gives the left rod 32g a single degree of freedom, in rotation about the axis of said left arm pivot 35g. The movements of the first and second left frames in the excitation direction are therefore opposed. The in-phase movement of these two masses is practically blocked. However, it may be observed for a very low amplitude and a vibration mode pushed back to higher frequencies (>40-50 kHz) than the operating frequency.

(34) The position of the left arm pivot 35g along the left rod 32g is determined in such a way that the moments of force exerted by gravity (directed along the excitation axis) on the left arm by the first and second left inertial masses about the left arm pivot 35g compensate for one another.

(35) FIG. 11 illustrates how the moments of force are evaluated. In the embodiment illustrated, the mass m.sub.2 of the second left inertial mass 12.sub.g2 is greater than the mass m.sub.1 of the first left inertial mass 12.sub.g1. V is the vertical direction and is directed upward. The moments of force that are exerted by the masses m.sub.1 and m.sub.2 are therefore m.sub.1.Math.d.sub.1 and m.sub.2.Math.d.sub.2 and the position of the left arm pivot 35g is determined so that these moments are of the same amplitude and oppose one another.

(36) If m.sub.1 and m.sub.2 are equal, then the left arm pivot 35g is therefore midway along the length of the left arm.

(37) The position of the left arm pivot 35.sub.g along the left arm is thus preferably determined so that the moments of force exerted by gravity on the left arm by the first and second left inertial masses about the left arm pivot 35.sub.g are substantially identical when the left arm, horizontal, is resting on the left arm pivot 35.sub.g, and the position of the right arm pivot 35.sub.d along the right arm is preferably determined so that the moments of force that are exerted by gravity on the right arm by the first and second right inertial masses about the right arm pivot 35.sub.d are substantially identical when the right arm, horizontal, rests on the right arm pivot 35.sub.d.

(38) Said local reductions in the left prongs 34.sub.g1 and 34.sub.g2 make it easier for the left rod 32g to effect a rotational movement about the left arm pivot 35g.

(39) The left prongs 34.sub.g1 and 34.sub.g2 have high stiffness in the excitation direction X, compared with the equivalent stiffnesses, in this direction, of the guide springs and of the left arm pivot 35g. This stiffness of the left prongs 34.sub.g1 and 34.sub.g2 opposes movements of the left inertial masses in that direction.

(40) The left prongs 34.sub.g1 and 34.sub.g2 have a torsional stiffness, about an axis parallel to the direction Z, that is less than or equal to that of the left arm pivot 35g.

(41) As depicted in FIGS. 4 to 7, the rod is preferably substantially nondeformable in service.

(42) The stiffness conferred by the left arm advantageously means that forces resulting from external vibrations and that are exerted on the first and second left inertial masses 12.sub.g1 and 12.sub.g2 can be opposed.

(43) The left arm is preferably made of a material chosen from silicon Si, SiN, SiC, quartz, and more generally any material used for creating MEMS structures.

(44) The left arm preferably has a length L.sub.30 greater than 100 microns, preferably greater than 200 microns, preferably greater than 300 microns, preferably greater than 400 microns, and/or less than 2000 microns, preferably less than 800 microns.

(45) The left arm preferably has a width l.sub.30 greater than 5 microns, preferably greater than 10 microns, preferably greater than 15 microns, and/or less than 50 microns, preferably less than 40 microns.

(46) The aspect ratio of the cross section of the rod of the left arm, namely the ratio length L.sub.30/width l.sub.30 is preferably less than 30.

(47) The thickness of the left arm, measured in the direction Z, when identical to that of the inertial masses, has little effect on how the left arm behaves. As a preference, the thickness of the arm is greater than 5 μm, the maximum thickness of the arm in practice being determined by the thickness of the substrate.

(48) The cross section of the rod, namely the cross section in a plane perpendicular to its length, can be any, for example rectangular or oval.

(49) The shape of the left arm is nonlimiting.

(50) The way in which the gyrometer behaves depends on the stiffness generated by the presence of the right and left arm pivots, of the left and right arms and of the mass thereof. A person skilled in the art however knows how to modify this stiffness, particularly by modifying the material of which the arms are made, or by modifying their dimensions, for example by modifying the width of the rods of the arms, and the shape of their cross sections. In practice, the stiffness can be modified by adjusting the characteristics of the prong and arm pivots.

(51) The mass of the left and right arms increases the inertia of the mechanical excitation mode: that may lead to a small drop in its resonant frequency. This phenomenon may be minimized if need be by altering the shape and material in order to obtain suitable stiffness characteristics for the structure.

(52) Simple tests can be used to check how the gyrometer behaves with a given shape of arm. These tests, which may for example be simulated using the finite element method, make it possible to identify unbalanced vibration modes and evaluate the resonant frequencies thereof.

(53) The lowest resonant frequency of the unbalanced mechanical modes determines the upper frequency band limit or “pass band” limit within which the gyrometer is substantially insensitive to external vibrations, within the limit of a given amplitude (for example 10 g) of vibrations.

(54) Such tests have demonstrated that the preferred characteristics hereinabove advantageously allow balanced mechanical modes to be offered out to very high external vibrational frequencies.

(55) As a preference, the arms are shaped to maintain to this balance out to external vibrational frequencies greater than 30 kHz and preferably greater than 40 kHz.

(56) The stiffness of the arms influences the resonant frequencies in the excitation direction X.

(57) The mechanical coupling provided by the arms means that two adjacent masses considered from among the first inertial masses and second inertial masses oscillate in pairwise phase opposition in the excitation direction X at the one same resonant frequency f.sub.Da that are substantially equal to the resonant frequencies f.sub.Da1 and f.sub.Da2, which for first and second gyrometers that are identical are themselves likewise equal. The resonant frequencies of the unbalanced modes are advantageously pushed out beyond 45 kHz in simulations. In the event that the first and second gyrometers are not identical, a resonant frequency in antiphase along the excitation axis appears in an intermediate frequency range (f.sub.Da1 and f.sub.Da2).

(58) The left and right arms have substantially nil effect on the vibration mode of the central masses in the detection direction.

(59) For the untuned mode, the arms are preferably shaped in such a way that the difference between the resonant frequency f.sub.Da in the excitation direction X, in the mode of oscillation in phase opposition, and any one of the resonant frequencies of the first central masses, in the detection direction, and/or any one of the resonant frequencies of the second central masses, in the detection direction,

(60) is greater than 1 kHz.

(61) Advantageously the width of the pass band is thereby increased.

(62) This feature of the gyrometer according to the invention distinguishes it in particular from gyroscopes, for which what is conventionally sought is a minimal difference, preferably a zero difference, between the resonant frequencies in the excitation direction and in the detection direction.

(63) As a further preference, the arms are shaped in such a way that the resonant frequency f.sub.Da in the excitation direction X, in the mode of oscillation in phase opposition, is less than any one of the resonant frequencies in the detection direction. This embodiment is particularly advantageous for the untuned mode.

(64) As a preference, the left arm is the only means of coupling between the first left inertial mass and the second left inertial mass. In particular, there is no coupling spring interposed between the first and second left frames.

(65) Advantageously, coupling using the left arm alone is relatively simple to achieve.

(66) Furthermore, this makes the first and second dual-mass gyrometers simpler to control.

(67) Moreover, the movements of the inertial masses of the first and second dual-mass gyrometers, driven by at least one actuator 17, for example by the first and second actuators 17.sub.1 and 17.sub.2 depicted symbolically (and only in FIG. 4 for the sake of clarity) are coupled by virtue of the arms and of the coupling springs. A single actuator can therefore be used to activate a desired vibration mode.

(68) As a preference, the first and second actuators 17.sub.1 and 17.sub.2 each comprise a sensor for measuring the amplitude of the movements, in the excitation direction X, of the first left and right inertial masses and of the second left and right inertial masses respectively, preferably a piezoresistive or capacitive measurement sensor, preferably piezoresistive.

(69) For a single-axis gyrometer, the measurements that the first and second detectors 24.sub.1 and 24.sub.2 provide may advantageously be compared against one another, preferably by a control module 26 common to the two dual-mass gyrometers, particularly in order to check that they are coherent with one another. In particular, if the difference between these measurements exceeds a predetermined threshold, the control module 26 may consider that at least one of the measures is erroneous and preferably issue an alarm accordingly.

(70) Finally, for a single-axis gyrometer, the acquisition of two measurements may be used to increase the sensitivity of the gyrometer.

(71) As a preference, the first and second detectors 24.sub.1 and 24.sub.2 comprise first and second sensors of the angular position of the first and second rocker respectively. These sensors are preferably first and second piezoresistive strain gages. These gages are set out in such a way as to deform under the effect of the movement of the first and second rockers 20.sub.1 and 20.sub.2 respectively.

(72) Such gages prove to be particularly reliable. In particular, inexplicably, the inventors have found that they provide more reliable measurements than capacitive gages in the presence of external vibrations.

(73) Other transducer components, for example capacitive gages, are, however, likewise conceivable.

(74) One gage is preferably fixed to at least one of the first and second rockers 20.sub.1 and 20.sub.2, as a preference, in order to increase the symmetry of the gyrometer and therefore its balance, on each of the first and second rockers 20.sub.1 and 20.sub.2. The measurements provided by the gages and by the actuator 17 for measuring the amplitude of the movements of the inertial masses 12.sub.g and 12.sub.d in the excitation direction X are preferably processed by the one same control module 26.

(75) Gages made completely or partially from metal, preferably aluminum or platinum, may also be used. As a preference, the gages are made of p-doped or n-doped silicon as that material gives a particularly high piezoresistive effect (a gage factor of 50 for a doping of a few 10.sup.19 cm.sup.−3, as compared with a gage factor of a few units for metals). Other doped semiconductors such as germanium may be envisioned.

(76) As a preference, these gages comprise piezoresistive nanowires connecting the first and second rockers 20.sub.1 and 20.sub.2 to respective anchor points which are fixed with respect to the substrate 10. A rocking movement of one rocker thus modifies the length of the nanowires and therefore the resistance of the nanowires. Measuring this resistance thus allows the angular position of the rocker about its rocker pivot to be evaluated.

(77) As a preference, a detector of one rocker, preferably of any one rocker, comprises two said nanowires positioned each on a respective side of the rocker pivot of said rocker so that a rocker movement that applies a tensile force to one of said nanowires at the same time applies a compressive action to the other of said nanowires.

(78) As a preference, the distance between the rocker pivot and any one of said nanowires is less than 100 μm, less than 60 μm, or less than 40 μm, and/or greater than 1 μm, greater than 10 μm, greater than 20 μm or greater than 30 μm. It is preferably used to adjust the resonant frequency in the detection direction. The effect that the nanowires have on the stiffness in this direction is effectively predominant. A low force applied, at the ends of the rocker, by the central masses may thus result in a high tensile or compressive force on the nanowires, as a result of the lever arm effect.

(79) The gages may also for example be capacitive gages.

(80) In one embodiment, the gyrometer comprises a sensor of the angular position of at least one of the left and right arms. Said sensor is preferably a piezoresistive strain gage or a capacitive gage, preferably a piezoresistive strain gage. The strain gages described hereinabove may be used.

(81) The sensor preferably comprises at least one nanowire (not depicted in figures), connecting said arm to the substrate, preferably at least left and right nanowires connecting the left arm and the right arm to the substrate respectively.

(82) The sensor of the angular position of at least one of the left and right arms may advantageously replace the measurement sensors conventionally used for measuring the amplitude of the movements, in the excitation direction X, of the first left and right inertial masses and of the second left and right inertial masses respectively. In particular, in this embodiment, control of the movement in the excitation direction and measurement of the movement in the detection direction may be controlled by one same electronic control unit, for example by time division multiplexing of the two channels.

Example

(83) Finite element simulations were conducted.

(84) The gyrometer was subjected to external vibrations, at increasing frequencies. The way in which the gyrometer behaved was observed. This is illustrated for certain notable frequencies in FIGS. 4 to 7.

(85) FIG. 6 illustrates a first possible mode of operation referred to as “working balanced drive” in which the first and second dual mass gyrometers 5.sub.1 and 5.sub.2 are each in the phase opposition mode in the direction of excitation and in the detection direction, the first and second left inertial masses are in phase opposition in the excitation direction and in the detection direction, and the first and second right inertial masses are in phase opposition in the excitation direction and in the detection direction.

(86) The first left inertial mass is in phase with the second right inertial mass. The second left inertial mass is in phase with the first right inertial mass. The assembly made up of the first left inertial mass and of the second right inertial mass is in phase opposition with the assembly made up of the second left inertial mass and of the first right inertial mass.

(87) The mechanical mode is balanced and is therefore ideally insensitive to external vibrations, the frequency of the oscillations being 20.5 kHz. The “working balanced drive” mode is the preferred mode of operation. It corresponds to the “normal” mode of operation, in the absence of external vibrations.

(88) FIG. 5 illustrates a second embodiment referred to as “second balanced drive”, in which the first and second dual mass gyrometers 5.sub.1 and 5.sub.2 are each in the mode in phase in the direction of excitation and in the detection direction, the first and second left inertial masses are in phase opposition in the detection direction and in the excitation direction, the first and second right inertial masses are in phase opposition in the detection direction and in the excitation direction.

(89) The mechanical mode is balanced, the frequency of oscillations being 22.8 kHz. It is ideally insensitive to external vibrations.

(90) FIG. 4 illustrates a third possible mode of operation referred to as “first balanced drive”, in which the first and second dual mass gyrometers 5.sub.1 and 5.sub.2 are each in the phase opposition mode in the detection direction and in the excitation direction, the first and second left inertial masses are in phase in the detection direction and in the excitation direction, and the first and second right inertial masses are in phase in the detection direction and in the excitation direction.

(91) The mechanical mode is balanced, the frequency of the oscillations being 46.3 kHz. It is ideally insensitive to external vibrations.

(92) FIG. 7 illustrates a fourth mode of operation referred to as “sensitive drive”, in which the first and second dual mass gyrometers 5.sub.1 and 5.sub.2 are each in the mode in phase in the detection direction and in the excitation direction, the first and second left inertial masses are in phase opposition in the detection direction and in phase in the excitation direction, and the first and second right inertial masses are in phase opposition in the detection direction and in phase in the excitation direction.

(93) The mechanical mode is unbalanced. The mode of oscillation in phase of the first and second dual mass gyrometers 5.sub.1 and 5.sub.2 in the excitation direction can thus be activated by external vibrations. In the absence of arms, the amplitude of the oscillations would be several orders of magnitude higher and the resonant frequency would be close to 20 kHz in the band of vibration frequencies that it is desired to exclude. According to the invention, the left and right arms provide the ability to oppose the efforts produced by the inertial forces resulting from the external vibrations and exerted on the frames of the first left and right inertial masses, and to the corresponding efforts exerted on the frames of the second left and right inertial masses, respectively. The arms advantageously provide the ability to oppose activation of this mode of operation under the effect of external vibrations.

(94) Remarkably, this imbalance appears only at a frequency of oscillation of around 47.6 kHz because of the presence of the left and right arms which provide a significant additional amount of mechanical stiffness along the excitation axis, and which oppose movement in the mode. However, modifications to the mechanical characteristics of the arms, particularly the strength or width of the arms or the stiffness of the arm pivots allows this frequency of imbalance to be pushed back further still.

(95) These performance aspects demonstrate that a gyrometer according to the invention is well suited to a harsh vibratory environment such as that of a motor vehicle engine or that of a machine tool. The large tolerance to vibration advantageously allows greater flexibility in the siting of the gyrometer in its position of use.

(96) Two-Axis Gyrometer

(97) The invention is not restricted to a single-axis gyrometer and also extends to a two-axis gyrometer able to measure rotation rates about axes of rotation parallel to two predefined directions.

(98) FIG. 10 illustrates a two-axis gyrometer according to the invention, able to measure rotation rates about axes of rotation parallel to the direction Y and/or to the direction Z.

(99) The gyrometer according to this embodiment is similar to the single-axis gyrometer according to the invention described hereinabove, but comprises a first dual mass gyrometer 5.sub.1 of the type of that of FIGS. 8 and 9, and a second dual mass gyrometer 5.sub.2 of the type of that of FIGS. 1 to 3.

(100) In particular, like the single-axis gyrometer according to the invention, it comprises left 30.sub.g and right 30.sub.d arms mounted to rotate on the substrate about a left-arm pivot 35.sub.g and a right-arm pivot 35.sub.d, respectively, the left arm mechanically coupling the frames of the first left inertial mass 12.sub.g1 and of the second left inertial mass 12.sub.g2, and the right arm 30.sub.d mechanically coupling the frames of the first right inertial mass 12.sub.d1 and of the second right inertial mass 12.sub.d2.

(101) Gyrometer with Monobloc Second Left and Right Inertial Masses

(102) In the preferred embodiment described above, the left arm mechanically couples first and second left frames and the right arm mechanically couples first and second right frames, the second left and right frames belonging to a second dual-mass gyrometer.

(103) In a variant illustrated in FIG. 12, the second left and right inertial masses do not belong to a dual-mass gyrometer but are monobloc left and right masses mounted with the ability to slide along a second axis X.sub.2 (corresponding to the “second excitation axis” of the embodiment in which the second left and right inertial masses belong to a second dual mass gyrometer). As a preference, the second left and right inertial masses are guided by guide springs so that they can move only in sliding along the second axis.

(104) The monobloc second masses and the positions of the arm pivots are preferably determined in such a way as to form, with the first inertial masses, for each arm, “balanced assemblies” namely assemblies in which the moments of force exerted by gravity, oriented in the excitation direction, on the right arm by the first and second right inertial masses about the right arm pivot compensate for one another, and in which the moments of force exerted by gravity, oriented in the excitation direction, on the left arm by the first and second left inertial masses about the left arm pivot compensate for one another.

(105) Advantageously, monobloc second left and right inertial masses are able to balance the loads produced by the vibrations on the frame of the first left and right inertial masses. That means that the mechanical structure can be given greater symmetry.

(106) As illustrated in FIG. 13, a gyrometer according to the invention may comprise several monobloc left and right masses assemblies. In each assembly, the monobloc left and right masses are mechanically coupled to the first left and right frames respectively by left and right arms respectively.

(107) As a preference, the gyrometer comprises exactly two said assemblies, preferably arranged symmetrically with respect to the first excitation axis X.sub.1, as in FIG. 13. Advantageously, the dimensions of the monobloc left and right masses and of the left and right arms can be reduced.

(108) As illustrated in FIGS. 14 and 15, the monobloc second left and right inertial masses of one assembly may be coupled by a second coupling spring 14.sub.2. Advantageously, the second coupling spring allows the resonant frequency of the drive mode of the entire gyrometer structure to be pushed out to a level comparable with that of the structure without the second left and right inertial masses. This coupling spring offers an additional degree of freedom for the left and right coupling.

(109) As is now clearly apparent, a gyrometer according to the invention offers remarkable resistance to vibrations. Furthermore, it is compact, reliable, notably thanks to the use of piezoresistive sensors, and offers improved sensitivity.

(110) A single axis gyrometer according to the invention in particular allows double measurement of a rotation rate.

(111) Of course, the invention is not restricted to the embodiments described and depicted, which have been provided merely for illustrative purposes.

(112) In particular, other known techniques for limiting the effects of external vibrations can be implemented, to supplement the invention.

(113) The first and second dual mass gyrometers of a single-axis gyrometer according to the invention may be of the type of FIGS. 8 and 9.

(114) At least one coupling spring needs to be provided between the first left and right inertial masses or between the second left and right inertial masses. The simultaneous presence of a first coupling spring between the first left and right inertial masses and of a second coupling spring between the second left and right inertial masses is optional.