Gyroscopic measurement method and sensor

Abstract

Measurement method and gyroscopic sensor The present invention relates to a sensor (10) comprising a housing (12) and a vibrating element (15) capable of vibrating relative to the housing (12), comprising: an initialization (410), to provide a pilot amplitude (xmax), a detection amplitude (ymax), an adjustment control (Tth) of predetermined spectral signature, and an angular velocity calibration (Ωcal);a calibration (420), comprising the control of the pilot amplitude and the vibration detection amplitude of the vibrating element (15) along the direction (x) of the pilot mode and the direction (y) of the detection mode, and simultaneously the exercise of a first stable force (Fy,phase,suppapp) configured so as not to disturb the measurement of the sensor (10) from the adjustment command (Tth), as well as the exercise of a second force (Fy,quadapp) determined on the basis of the spectral signature of the adjustment command to cause a rotation of the direction of the pilot mode, an instantaneous angular velocity (Ω(t)) of the housing (12) being imposed equal to the calibration angular velocity (Ωcal), and the determination of a reference angular velocity (Ωref); an acquisition (430), analogous to the calibration but with a free instantaneous angular velocity (Ω(t)); a determination (440) of a measured instantaneous angular velocity (Ωmes(t)). Figure for the abbreviation: 3;

Description

Title of the invention: Gyroscopic measurement method and sensor

[0001] The present invention relates to a gyroscopic measurement method.

[0002] The invention also relates to a gyroscopic sensor for implementing the gyroscopic measurement method, as well as a computer program comprising instructions that lead the sensor to perform the step of determining the instantaneous angular velocity of the gyroscopic sensor of this method.

[0003] A Coriolis Vibratory Gyroscope (CVG) sensor allows measurement of the component along an axis, called the sensitivity axis, of an instantaneous rotation velocity vector of a reference frame attached to a sensor housing with respect to an inertial reference frame.

[0004] The CVG comprises for this purpose a vibrating element of the sensor, capable of vibrating relative to the housing. The measurement is carried out thanks to the effects of the Coriolis inertial force exerted on the vibrating element.

[0005] The vibrating element of a CVG is capable of vibrating along two coplanar vibration directions, called the pilot mode direction and the detection mode direction, the work of the Coriolis force allowing a transfer of mechanical energy between the two directions.

[0006] The sensitivity axis of the CVG is orthogonal to the plane of the directions of the pilot mode and the detection mode.

[0007] For the measurements, the vibrating element is excited along the pilot mode direction at its resonant frequency by the excitation system. The amplitude of the vibrations along the pilot mode is kept constant by means of a feedback control system for the voltage applied to the excitation system. Any variations in the resonant frequency, particularly those related to variations in the temperature of the vibrating element, are monitored by means of a frequency feedback control system.

[0008] If the component along the sensitivity axis of the instantaneous rotational velocity vector of the housing with respect to an inertial reference frame is non-zero, the displacement of the vibrating element along the pilot mode direction generates a Coriolis force. This force excites the vibrating element along the detection mode direction, with an amplitude that is proportional to the component along the sensitivity axis of the instantaneous rotational velocity vector.

[0009] A CVG can operate in two modes: gyroscope mode and gyrometer mode.

[0010] In gyroscope mode, the position of the pilot mode direction in the vibration plane is free. The instantaneous rotational speed to be measured is then deduced from the angular position of the vibration plane of the vibrating element in the reference frame attached to the housing.

[0011] In gyroscope mode, the direction of the pilot mode in the plane of vibration is controlled by sending an electronic command and the instantaneous rotation speed to be measured is deduced from the force to be exerted to control this direction.

[0012] Whether the CVG is used in gyroscope mode or gyrometer mode, the measurements are affected by intrinsic errors related to defects in the CVG. Among these defects, we can mention the anisotropies of stiffness or damping of the vibrating element, defects in the excitation control electronics or the position detection electronics of the vibrating element, defects in the electrical reference voltage for the excitation, etc.

[0013] Among these errors, some are called harmonic because they are proportional to cosine or sine functions of an angle that is an even multiple of the angle characterizing the direction of the pilot mode in the reference frame linked to the housing.

[0014] US 6 598 455 describes a method of gyroscopic measurements in which the geometric vibration position of the gyroscope is intentionally modified by electrostatic means over time, in order to improve the calibration of the gyroscope.

[0015] US 7 093 370 further describes a MEMS gyroscope in which an angular velocity is intentionally imposed on the sensor by mechanical means, the direction of rotation of the sensor being periodically alternated in order to reduce measurement errors and in particular scaling factor errors of the gyroscope.

[0016] FR 2937414 describes a vibrating gyroscope that combines the principles of US patent 6,598,455 by injecting an electronic signal to rotate the vibration wave and US patent 7,093,370 by imposing a periodically alternating electrical rotation to minimize harmonic errors. The control signal is adapted to rotate the geometric vibration position of the gyroscope in one direction for a portion of the control signal period according to a first velocity profile, and then in the opposite direction according to a second velocity profile. The vibrating gyroscope then provides a corrected signal based on the difference between the measurement signal and the control signal.

[0017] However, due to errors in the chain converting the control signal into an electrostatic force, the force actually applied to the vibrating element of the gyroscope to obtain its alternating rotation is different from the force that should theoretically be obtained from the control signal.

[0018] If the errors of the conversion chain are perfectly stable over time, the error made on the angle measurement can be zero over a period characteristic of the variations of the control signal.

[0019] However, this is very unlikely, as the sources of error are numerous and of different kinds. These include, in particular, errors in the detection of the combs of detection, excitation errors of the excitation combs as well as instabilities of the reference voltage used for the operation of these combs, and errors of the electronic boards which coordinate the implementation of the gyroscopic measurement process.

[0020] Ultimately, in most situations, the average value of the error is not zero over a period of the alternating rotation of the sensor's position. Furthermore, during the round trip of the wave, the angular errors of the sensor are greater the more significant the aforementioned defects are.

[0021] Such a device reduces the impact of defects on the measurement without however allowing the measurement error related to these defects to be evaluated.

[0022] Furthermore, the control signal used in FR 2937414 must allow the gyroscope to return to the same angular position between the beginning and end of the control period. In cases where the gyroscope is moving in the inertial frame of reference and not at rest, such a signal will not allow both a zero-average control signal and a return to the same angular position.

[0023] An object of the invention is then to propose a gyroscopic measurement method in which an alternating rotation of the directions of the pilot and detection modes of the gyroscopic sensor is controlled, and in which measurement errors, in particular the scale factor error, are reduced.

[0024] To this end, the invention relates to a gyroscopic measurement method using a sensor comprising a housing and a vibrating element capable of vibrating relative to the housing in a plane of vibration simultaneously along a pilot mode direction and along a detection mode direction different from the pilot mode direction, the method comprising the following steps: - initialization, during which a pilot amplitude, a detection amplitude, an adjustment command with a predetermined spectral signature, and a calibration angular velocity are provided; - calibration, including: i) the control of a first vibration amplitude in a forced sinusoidal regime of the vibrating element along the direction (x) of the pilot mode, ii) simultaneously, the application of a first stable force on the vibrating element configured so as not to disturb the measurement of the sensor from the adjustment control, and the control of the detection amplitude of a second vibration amplitude of the vibrating element along the direction of the detection mode; iii) simultaneously, the application of a second force on the vibrating element, following the direction of the detection mode and in quadrature phase with the first force, the second force being determined on the basis of a third force which estimates the force actually applied to control the second amplitude and the spectral signature of The adjustment control is configured to cause a rotation of the pilot mode direction relative to the housing. an instantaneous angular velocity of the housing with respect to a sensitive axis being imposed and equal to the calibration angular velocity during i), ii) and iii); iv) the determination of a reference angular velocity from the calibration angular velocity and vibration measurements of the vibrating element during iii); - acquisition, including i), ii) iii) calibration with a free instantaneous angular velocity; - determination of an instantaneous angular velocity measured of the housing with respect to the sensitive axis from measurements of the vibrations of the vibrating element during acquisition and the reference angular velocity.

[0025] In the method according to the invention, an adjustment control is used to apply to the vibrating element a first force along the direction of the detection mode, in phase with the vibrations following the pilot mode.

[0026] The control of the amplitude of the vibrations according to the detection mode is done in the presence of the first force and allows the second determination module to implicitly estimate the first force.

[0027] The first force is stable and configured so as not to disturb the measurement performed by the sensor.

[0028] A second force is then exerted from this estimator, in quadrature with the first force along the direction of the sensor's detection mode.

[0029] This method of obtaining the second force allows for good stability of the second force.

[0030] The second force is, as in the prior art, controlled to cause an additional rotation of the directions of the pilot mode and the detection mode, in addition to the rotation related to the Coriolis force in order to reduce the harmonic errors of the sensor.

[0031] The calibration step makes it possible to determine a reference angular velocity from which the measured angular velocity will subsequently be determined without an explicit value of the second force being used at any time, and this thanks to the particular and stable method of obtaining the second force.

[0032] Unlike French patent FR 2937414, the measurement is derived from the measurement signal not by removing an injected signal intended to recreate a precession force, but by removing a precession command resulting from the projection of a force obtained through the servo systems. This force is implemented to counteract the injection of a very stable force intentionally applied to the sensor. In other words, to obtain the angular velocity at the output, an unstable controlled signal is not subtracted from the measurement, but rather the image of a very stable force. design.

[0033] Measurement errors, in particular the error related to the scale factor, are therefore reduced.

[0034] According to an advantageous aspect of the invention, the calibration comprises: i) the control of a first vibration amplitude in a forced sinusoidal regime of the vibrating element along the direction of the pilot mode, ii) simultaneously, the application of a first force on the vibrating element, along the direction of the detection mode and in phase with the vibrations of the vibrating element along the direction of the pilot mode, from the adjustment control and the servo-control to the detection amplitude of a second amplitude of vibrations of the vibrating element along the direction of the detection mode, iii) simultaneously, the application of a second force on the vibrating element, following the direction of the detection mode and in quadrature phase with the first force, the second force being determined on the basis of a third force which estimates the force actually applied to control the second amplitude and the spectral signature of the adjustment control and configured to cause a rotation of the pilot mode direction relative to the housing, an instantaneous angular velocity of the housing relative to a sensitive axis being imposed and equal to the calibration angular velocity during i), ii) and iii), and the acquisition includes i), ii) iii) calibration with a free instantaneous angular velocity.

[0035] According to other advantageous aspects of the invention, the gyroscopic measurement method comprises one or more of the following features, taken individually or in all technically possible combinations:

[0036] - for calibration, the first force is exerted on the vibrating element, according to the direction of the detection mode and in phase with the vibrations of the vibrating element following the direction of the pilot mode;

[0037] - the calibration angular velocity is zero;

[0038] - the detection amplitude is zero;

[0039] - the determination of the second force during calibration and during acquisition include a filtering of the third force which estimates the actual force exerted to control the second amplitude;

[0040] - the first force is exerted by means of an electrostatic device configured to exert a force directly proportional to a position of the vibrating element according to the direction of the pilot mode and function of the adjustment control;

[0041] - the adjustment command is of the form: r'h = To + Tfio^e) + T2cos(20 + ... + Tncos(«5) where n is a strictly positive integer, T; for i an integer between 1 and n denotes a constant term and 0 denotes an angular position of the pilot mode direction relative to a reference axis of a frame linked to the housing, the reference axis being orthogonal to the sensitive axis;

[0042] - a first adjustment command is provided during a first interval of time and a second adjustment command which is the opposite of the first adjustment command is provided during a second time interval, so that the direction of the pilot mode relative to the case rotates in one direction during the first time interval and in the opposite direction to the first during the second time interval.

[0043] The invention also relates to a gyroscopic sensor comprising: - a case; - a vibrating element capable of vibrating relative to the housing in a plane of vibration simultaneously along a direction of a pilot mode and along a direction of a detection mode different from the direction of the pilot mode; - a first servo module, configured to receive a pilot amplitude and to servo a first amplitude of vibrations in forced sinusoidal regime of the vibrating element to a predetermined pilot amplitude following the direction of the pilot mode; - a second servo module configured for: a) exert on the vibrating element a first stable force configured so as not to disturb the sensor measurement from an adjustment command whose spectral signature is predetermined, b) to control a second vibration amplitude of the vibrating element along the direction of the detection mode, according to a predetermined detection amplitude, and (c) exert a second force on the vibrating element, following the direction of the sensing mode and in quadrature phase with the first force, the second force being configured to cause a rotation of the direction of the pilot mode relative to the housing, the second force being determined on the basis of a third force which is an estimate of the force actually exerted to control the second amplitude and of the spectral signature of the adjustment control; - a measurement module configured to generate vibration measurements of the vibrating element along the x direction of the pilot mode and the y direction of the detection mode and to exchange information with the first servo module and with the second servo module; - a determination module configured to exchange information with the measurement module and the first and second control modules and to determine: i) a reference angular velocity derived from a calibration angular velocity predetermined and based on vibration measurements of the vibrating element 15 transmitted by the measuring module in a calibration mode for which an instantaneous angular velocity of the housing relative to a sensitive axis is imposed and equal to the calibration angular velocity, and ii) an instantaneous angular velocity measured of the housing with respect to the sensitive axis from measurements of the vibrations of the vibrating element in an acquisition mode in which the instantaneous angular velocity is free and from the reference angular velocity.

[0044] According to another advantageous aspect of the invention, the first servo module and the second servo module include electrostatic excitation means.

[0045] The invention also relates to a computer program comprising instructions which lead the sensor according to one of the preceding embodiments to execute the process according to any one of the embodiments described above.

[0046] 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:

[0047] [Fig-1] [Fig.1] is a schematic representation of a CVG according to the invention;

[0048] [Fig.2] [Fig.2] is a schematic representation of the operation of the CVG of earlier art.

[0049] [Fig.3] [Fig.3] is a schematic representation of the operation of the CVG of the [Fig.l];

[0050] [Fig.4] [Fig.4] is a schematic representation of the trajectory of the element vibrating from the [Fig.l] and the directions of its pilot and detection modes in a spatial reference frame linked to the housing;

[0051] [Fig. 5] [Fig. 5] is a flowchart representation of a process according to the invention;

[0052] [Fig. 6] [Fig. 6] is a partial representation of an electrostatic device of excitement.

[0053] [Fig.7] [Fig.7] is a flowchart representation of a process of the prior art implemented on the CVG of the [Fig.2];

[0054] [Fig.8] [Fig.8] is a detailed flowchart representation of the acquisition step 430 of the process of the [Fig.5].

[0055] The Coriolis effect gyroscopic sensor 10, designated by the abbreviation CVG in the following, according to the invention is described with reference to [Fig.1].

[0056] The CVG 10 comprises a housing 12 and a vibrating element 15 capable of vibrating relative to the housing 12.

[0057] The CVG 10 is, for example, implemented as a microelectromechanical system (in English, "Micro Electromechanical Sensor," MEMS). The vibrating element 15 and the housing 12 are then machined from a block of silicon or quartz by micromachining, and the vibrating element 15 is set into vibration by an electrical process. This arrangement minimizes the size and / or manufacturing cost of the CVG 10.

[0058] Three axes X, Y, Z of the XYZ space frame of a reference frame (XYZ, t) linked to the housing 12 are represented on the [Fig.4], the Z axis being of fixed direction in a space frame of an inertial reference frame.

[0059] The CVG 10 is configured to measure an instantaneous angular velocity Q(t) of the sensor with respect to the Z axis, which therefore constitutes the sensitivity axis (or equivalently the sensitive axis) of the CVG 10.

[0060] To this end, the vibrating element 15 comprises a test mass M, capable of vibrating in the XY plane along two directions x and y, with a natural frequency co0x, respectively co0y close to co0x-

[0061] In the following, we consider that the x direction is the direction of the pilot mode and that the y direction is the direction of the detection mode.

[0062] As can be seen in [Fig.4], the angular position of the x direction of the pilot mode is located by the angle 0 defined with respect to the reference axis X of the space frame (XYZ) linked to the housing 12.

[0063] The test mass M is capable of vibrating along the x direction of the pilot mode x and the y direction of the detection mode, with a resonance frequency co close to co0x-

[0064] The CVG 10 includes a first control module 20 capable of controlling a characteristic vibration amplitude of the vibrating element 15 to a predetermined non-zero pilot amplitude x max, the vibrating element 15 vibrating in forced sinusoidal regime at the resonance pulsation co along the direction x of the pilot mode, from measurement data of the position of the vibrating element along the direction x of the pilot mode.

[0065] The first control module 20 includes conventional means for controlling the amplitude of the vibrations of the vibrating element 15 according to the pilot mode. These means are not shown in detail in the figures. They include, for example, the control means described in document EP2960625.

[0066] By way of example, which will be called a reference example in the following, the first servo module 20 includes an electrostatic device 20A configured to exert a first force Fx>ass in the x direction of the pilot mode on the vibrating element 15. The first force Fx ass is then proportional to a first amplitude command.

[0067] The electrostatic device 20A and the test mass M of the vibrating element 15 form, by way of example, a set of interdigitated combs, as shown in [Fig. 6]. The first amplitude control is a voltage Vexc,x(t) imposed on the electrostatic device 20A by the servo module 20.

[0068] In the case of [Fig.6], the force applied to the test mass M along the x direction of the pilot mode at a time t is of the form Fx>ass (t)=fgeOmVexc,x2(t) where: - fgeom is a factor that is a function of the geometry of the combs, and - Vexc,x is the voltage imposed by the generator.

[0069] In general, the voltage VexC,x is of the form VexC,x (t) = VOx + V[x cos (eut). Thus, the force actually applied to the test mass M, after filtering out the terms with angular frequency 2co, is of the form:

[0070] [Math.l] Fx,ass(t) = fgeom (Vqx + j V Lv + (Mt))

[0071] The constant term of this force is not used hereafter, since only the last term allows the test mass M to oscillate. In other words, the non-sinusoidal terms are either naturally filtered or filterable by a suitable filtering stage.

[0072] In the end, it is therefore understood that the electrostatic device 20A can be configured by a person skilled in the art to exert a first force Fx>ass of pulsation substantially equal to the natural pulsation co0x of the vibrating element 15 according to the pilot mode, from a suitably chosen amplitude control, to obtain the control of the amplitude of the vibrations of the vibrating element 15 to the pilot amplitude xmax.

[0073] The first servo module 20 includes in the reference example a processor or a programmable logic circuit (such as a "Field Programmable Gate Array", FPGA), configured to manage the servo control of the first amplitude command, as well as a proximity card configured to inject the first amplitude command signal into the electrostatic device 20A.

[0074] The processor or programmable logic circuit is advantageously configured to manage the control of the vibration pulse of the vibrating element 15 along the x direction of the pilot mode, for example to the resonance pulse co.

[0075] The CVG 10 includes a second control module 25 capable of controlling a characteristic amplitude of vibrations of the vibrating element 15 along the y direction of the detection mode to a detection amplitude ymax, the vibrating element 15 vibrating in forced sinusoidal regime along the y direction of the detection mode at the resonance pulsation co, from measurement data of the position of the vibrating element along the y direction of the detection mode.

[0076] To this end, the second control module 25 may include control means similar to those of the first control module 20 (not shown in detail).

[0077] Thus, in the reference example, the second servo module 25 includes an electrostatic device 25A configured to exert on the element Vibrating 15, a second force Fy>phase>ass, whose direction is the y direction of the detection mode, is in phase with the vibrations following the x direction of the pilot mode. The second force FyjPhase ass is then proportional to a second amplitude control, based on the principle described for the first servo module 20.

[0078] The second control module 25 includes, in the reference example, a processor or a programmable logic circuit (such as a Field Programmable Gate Array, FPGA), configured to manage the control of the second amplitude command. The second control module 25 also includes a proximity card, configured to inject the second amplitude command signal into the electrostatic device 25A.

[0079] The processor or programmable logic circuit in the reference example is the same as that of the first servo module 20. This arrangement is advantageous but not mandatory.

[0080] The processor or programmable logic circuit is advantageously configured to manage the control of the vibration pulse of the vibrating element 15 according to the y direction of the detection mode, for example to the resonance pulse co.

[0081] The proximity card in the reference example is the same as that of the first servo module 20. This arrangement is advantageous without being mandatory.

[0082] The second servo module 25 includes an adjustment control unit 26, capable of receiving an adjustment command Tth and of exerting from the adjustment command Tth an additional force Fyphasesuppapp whose direction is the y direction of the detection mode, in phase with the vibrations of the vibrating element 15 along the x direction of the pilot mode.

[0083] The spectral signature of the adjustment control Tth, that is to say its Fourier series decomposition, is known. The coefficients Ti to Tn (n a strictly positive integer) of equation (a) below are therefore known.

[0084] Tth = To + Z jcos(60 + T9cos(20 + ... + T„cos(n0) (a)

[0085] To this end, the adjustment control unit 26 may include an electrostatic device 26A configured to actually exert an additional force Fy phase supp “pp of the form Fyphasesupp“pp =T“ppx in response to the adjustment command Tth, x being the position of the test mass M according to the direction of the pilot mode.

[0086] Typically, the electrostatic device 26A is a trimming comb biased by a very stable bias voltage VT and capable of exerting a force in the direction of the detection mode, directly proportional to the position x of the test mass M along the direction of the pilot mode and proportional to the square of the bias voltage VT. The expression "directly proportional" here means that it is not necessary to measure or reconstruct the position x of the test mass M according to the direction of the pilot mode, the force exerted by the adjustment comb spontaneously adjusting to this position.

[0087] Typically, a force F exerted by means of the adjustment comb is given by the following equation (b), in which K denotes a gain that depends only on the geometric characteristics of the adjustment comb:

[0088] F = VpCx (b)

[0089] This force is obtained by the physical design of the adjustment comb without it being necessary to estimate the position x of the test mass. It is therefore directly proportional to x.

[0090] It should be noted that the physical principle is entirely different from a force Faa which would be obtained, as in prior art devices, by means of an excitation comb following the direction of the pilot mode, which would be given by equation c):

[0091] =

[0092] where x denotes an estimator of the position x of the test mass and not the actual position x of this test mass.

[0093] The adjustment comb is a quadrature adjustment comb, that is to say a comb implies a coupling between the pilot mode and the detection mode.

[0094] Alternatively, the adjustment comb is a frequency adjustment comb, that is to say a physical device configured to modify at least one of the natural frequencies of the test mass M along the x and / or y directions.

[0095] The control of the amplitude of the vibrations of the vibrating element 15 along the y direction of the detection mode is achieved by the second control module 25 in the presence of the additional force FyjPhaSejSupPapp actually applied.

[0096] The second servo module 25 is also configured to actually apply a third force Fy>quadapp on the vibrating element 15, in the direction y of the detection mode and in quadrature phase with the additional force FyphasejSUppaPP, based on a spectral signature of the adjustment command Tth and an estimate FyjPhaseassest of the second force Fyjphaseassapp actually exerted by the second servo module 25 to control the characteristic amplitude of the vibrations of the vibrating element 15 along the direction y of the detection mode in the presence of the additional force Fy phasejSUppaPP in two cases of movement of the sensor 10: - a first case, for which the instantaneous angular velocity Q(t) of the housing 12 with respect to the sensitive axis Z of the sensor 10 in the inertial frame of reference is imposed, with a value equal to a predetermined calibration angular velocity Qcai, and - a second case, in which the instantaneous angular velocity Q(t) is free to establish itself under the effect of the movement of the casing 12, in particular linked to the movement of a The device on which the CVG 10 is implemented, and during which the instantaneous angular velocity Q(t) is therefore unknown a priori and must be determined. In this second case, the instantaneous angular velocity is therefore not imposed, in particular the predetermined calibration angular velocity Qcai, unlike the first case.

[0097] The first and second servo modules 20, 25 are configured to exchange data with a measurement module 30 of the CVG 10, for the purpose of controlling the vibrations of the vibrating element 15.

[0098] The measurement module 30 is capable of generating vibration measurements of the vibrating element 15 along the x directions of the pilot mode and y directions of the detection mode and is capable of exchanging information with the first servo module 20 and with the second servo module 25.

[0099] In particular, the measuring module 30 is capable of measuring the position x(t) (respectively y(t)) of the vibrating element 15 and / or its velocity dx / dt(t) (respectively dy / dt(t)) and / or its acceleration d2x / dt2(t) (respectively d2y / dt2(t)) along the direction x (respectively along the direction y).

[0100] To this end, the measuring module 30 includes, in the non-limiting reference example, electrostatic detection means 30A along the x direction of the pilot mode and electrostatic detection means 30B along the y direction of the detection mode.

[0101] Advantageously, the electrostatic detection means 30A and 30B each form with the test mass M a set of interdigitated combs, on the geometric principle represented in [Fig.6].

[0102] In the reference example, the proximity card is advantageously configured to amplify the signals detected by the measurement module 30 and to transmit the amplified signals to the processor or the programmable logic circuit.

[0103] The measurement module 30 is also configured to exchange information with a determination module 35 of the CVG 10.

[0104] The determination module 35 is capable of exchanging information not only with the measurement module 30 but also with the first and second control modules 20, 25.

[0105] The determination module 35 is capable of determining a reference angular velocity Qref from the calibration angular velocity Qcai as well as from measurements of the vibrations of the vibrating element 15 transmitted by the measurement module 30 to the first and second servo modules 20, 25 in the first case of movement of the sensor 10.

[0106] The determination module 35 is capable of determining, in the second case of movement of the sensor 10, an instantaneous measured angular velocity Qmes(t), which is an estimator of the desired angular velocity Q(t), from measurements of the vibrations of the vibrating element 15 transmitted by the measuring module 30 to the first and second servo modules 20, 25 and the reference angular velocity Qref.

[0107] We will now describe the process 400 according to the invention with reference to figures 3, 5 and 8, in comparison with the prior art process shown in figures 2 and 7.

[0108] The method 400 includes an initialization step 410, a calibration step 420, an acquisition step 430 and a determination step 440 of the instantaneous angular velocity measured Qmes(t).

[0109] Initialization step 410 includes: a) the supply to the first control module 20 of the non-zero pilot amplitude xmax to which the characteristic amplitude of the vibrations in forced sinusoidal regime of the vibrating element 15 along the x direction of the pilot mode must be controlled, b) the supply to the second control module 25 of the detection amplitude ymax to which the characteristic amplitude of the vibrations of the vibrating element 15 along the y direction of the detection mode must be controlled, (c) the provision to the adjustment control unit 26 of the adjustment control Tth, whose spectral signature is known, and d) the supply to the calibration angular velocity determination module 35 ^cal*

[0110] The detection amplitude ymax is for example zero.

[0111] The initialization step 410 is followed by the calibration step 420 during which: i) The characteristic amplitude of the vibrations of the vibrating element 15 vibrating in forced sinusoidal regime along the x direction of the pilot mode is controlled to the non-zero pilot amplitude x max by means of the first control module 20. The first control module 20 receives for this purpose measurements of the vibrations of the vibrating element 15 along the x direction of the pilot mode from the measuring module 30. ii) simultaneously, the additional force FyjphasejSuppaPP, whose direction is the y direction of the detection mode and in phase with the vibrations of the vibrating element 15 along the x direction, is exerted by the adjustment unit 26 from the adjustment control Tth and the characteristic amplitude of the vibrations of the vibrating element 15 along the y direction of the detection mode is controlled to the detection amplitude ymax by means of the second control module 25. The second control module 25 receives for this purpose measurements of the vibrations of the vibrating element 15 along the y direction of the detection mode and along the x direction of the pilot mode from the measuring module 30. iii) the second servo module 25 determines the third force Fy>quadapp to be exerted on the vibrating element 15, in the direction y of the detection mode and in quadrature phase with the additional force FyjPhaSejSupPapp, based on an es Timation FyjPhase assest of the second force Fy>phase>assapp actually exerted by the second servo device 25 to control the characteristic amplitude of the vibrations of the vibrating element 15 along the y direction in the presence of the additional force F y,phase,supPapp- The third force Fy>quad “pp is, as will be seen later, configured to control a rotation of the x, y directions of the pilot and detection modes relative to the housing 12. iv) the second control module 25 controls the exercise of the third force Fy>quadapp, the operating conditions of i) and ii) being maintained: the characteristic amplitude of the vibrations of the vibrating element 15 vibrating in forced sinusoidal regime along the direction x of the pilot mode is controlled to the non-zero pilot amplitude xmax by means of the first control module 20, and the characteristic amplitude of the vibrations of the vibrating element 15 along the direction y is controlled to the detection amplitude ymax in the presence of the additional force Fy suppapp phase actually applied, v) the determination module 35 determines the reference angular velocity Qref from the calibration angular velocity Qcai as well as the measurements of the vibrations of the vibrating element 15 transmitted by the measurement module 30 to the first and second control modules 20, 25 during iv.

[0112] In the example, the additional force Fy phaSe,SUppapp is exerted in the y direction of the detection mode and in phase with the vibrations of the vibrating element 15 along the x direction.

[0113] More generally, the additional force is applied by means of a device that provides a stable amplitude. Furthermore, the additional force is configured so as not to interfere with the measurement performed by the sensor.

[0114] More generally, the additional force is exerted by means of a device that provides a stable amplitude. Advantageously, said device is configured to exert an additional force whose amplitude is constant to within 10 ppm or less, that is to say, whose relative variations in amplitude are less than or equal to 1 / 100,000.

[0115] Furthermore, the additional force is configured so as not to interfere with the measurement performed by the sensor.

[0116] The calibration step 420 is followed by an acquisition step 430 reproducing steps i), ii), iii), and iv) of the calibration step, except that for the acquisition step 430, the instantaneous angular velocity Q(t) of the housing 12 with respect to the sensitive axis Z of the sensor 10 in the inertial frame of reference is not imposed. The movement of the sensor 10 therefore corresponds, for the acquisition step 430, to the second case of movement described above.

[0117] Following the acquisition step 430, the determination step 440 is implemented using the determination module 35: the determination module 35 determines the instantaneous angular velocity measured Qmes(t), which is an estimator of the instantaneous angular velocity Q(t) of the housing 12, from the vibration measurements of the vibrating element 15 transmitted by the measuring module 30 to the first and second servo modules 20, 25 during the acquisition step 430 and from the reference angular velocity Qref determined at the calibration step 420.

[0118] To better understand the method 400 according to the invention, the theory underlying the control of an alternating rotation with zero time average of the xyZ frame linked to the x, y directions of the pilot and detection modes with respect to the XYZ frame linked to the housing is described below.

[0119] To simplify the writing of the equations enabling understanding of the prior art process and the process 400 according to the invention, the vibrating element 15 is modeled in the following by a mass M suspended on a rigid frame C by means of two pairs of springs 15A, 15B of respective stiffnesses Kx and Ky, as shown in [Fig.1].

[0120] Furthermore, it is assumed in the following that the stiffness constants and natural frequencies of the vibrating element 15 are identical in pilot mode x and mode y. In this particular case, we can therefore write that Kx = Ky = K and that cüox = co0y = coq.

[0121] This simplification should in no way be considered as limiting the operation of the sensor 10 according to the invention, the following equations being able to be rewritten without difficulty in the most general case.

[0122] In general, the trajectory of the mass M in forced sinusoidal regime is an ellipse in the xyZ frame.

[0123] This ellipse is reduced to a straight line segment in the direction x of the pilot mode in the case where the amplitude of the vibrations according to the detection mode is controlled to a zero detection amplitude ymax.

[0124] Without making any assumption at this stage about the value of the detection amplitude ymax, the position x of the mass M along the direction x of the pilot mode as a function of the time t is of the form x(t) = xmaxcos (eut) and the position y of the mass M along the direction y of the detection mode as a function of the time t is of the form y(t) = ymaxsin (eut).

[0125] If the x direction of the pilot mode with respect to the X axis of the XYZ frame linked to the housing 12 is located by the angle 0 shown in [Fig.4], the coordinates X and Y of the mass m in the XYZ frame linked to the housing 12 are related to the coordinates x and y of the mass M in the xyZ frame by equation 2:

[0126] [Math.2] [X1_[cosf) - sinO 1 p 1_ « / a\P' LrJ Hx

[0127] in which R(0) is the change-of-basis matrix from the xyZ frame to the XYZ frame: [Math.3] 'cos3 . sinO -sind' cos 3 .

[0128]

[0129]

[0130]

[0131]

[0132]

[0133]

[0134]

[0135]

[0136]

[0137]

[0138] I) OPERATING EQUATIONS COMMON TO THE PRIOR ART PROCESS AND THE PROCESS 400 ACCORDING TO THE INVENTION In the prior art method shown in [Fig. 2], as in method 400 according to the invention, the transition matrix R(0) is a function of time. Indeed, in these methods, a rotation of the xyZ frame relative to the XYZ frame is controlled, thus a temporal evolution of the angle 0, in order to eliminate the harmonic errors of the CVG 10. Furthermore, in gyroscope mode, the angle 0 is free to evolve, and the control mechanisms are applied in the xyZ frame. The first time derivatives dX / dt and dY / dt of the X and Y coordinates of mass M therefore satisfy: [Math.4] [ Y] = 0 ■ ' LyJ \ The second time derivatives d2X / dt2 and d2Y / dt2 of the X and Y coordinates of mass M satisfy the following: [Math.5] ["Xl x-32x-23y-3y W \ fl2ÔX+ëx+y-è\ In a forced sinusoidal regime at angular frequency co, if we neglect the terms that are not proportional to a positive integer power of the angular frequency co compared to the other terms, equation 5 can be written in the simplified form of equation 6: [Math.6] X ÿ. ' x-23y 23x + ÿ In the frame of reference of the case 12, the mass M is subjected to the forces FtotjX and Ftot>y exerted respectively by the excitation devices 20A, 25A, to the restoring forces of the springs, as well as to a damping which is modeled by a fluid friction force along each of the directions x and y associated with a quality factor Q. The damping matrix A of the vibrating element 15, taking into account damping anisotropies, is of the form described in equation 7: [Math.7] [1 0 Q 10 1 "1 a2 ' .a2 -al. The stiffness matrix Kl of the vibrating element 15, taking into account anisotropies of stiffness, is of the form: [Math. 8] r2 "J 1 = ¾ -rlJ LO r2 ] -rl J

[0139] Furthermore, when the frame of reference of the housing 12 is undergoing a rotational motion of component Q(t) along the Z direction relative to the inertial frame of reference, the mass M, due to its non-zero relative velocity in the frame of reference of the housing 12, is subjected to a Coriolis inertial force in this frame of reference of the case 12.

[0140]

[0141]

[0142]

[0143]

[0144]

[0145]

[0146]

[0147]

[0148]

[0149]

[0150]

[0151]

[0152] Applying Newton's second law to the mass M in the non-inertial frame of reference of the casing gives equation 9: [Math.9] + a[^1 +2Q LYJ 'L Kl y To simplify the writing of the equations, damping anisotropies are neglected in the following, without this being a limitation for the implementation of the process. Neglecting damping anisotropies, equation 9, after multiplication by R(-0) and with the approximations of equation 5, can be written as follows: [Math. 10] In the case where the amplitude ymax of the vibrations according to the detection mode is controlled to ymax = 0, equation 10 takes the form: [Math. 11] 714^13^4^)17 =K. If we separate, along the x direction of the pilot mode, the terms in phase or opposite phase with the position x of the mass M from the terms in quadrature with this position, by decomposing FtotjX into: [Math. 12] Ftot^x — Fx,phax + Fx,quad We obtain system 13 equations: [Math. 13] ' (rlcos(20) +r2sin(20)}x~F^phaxe (1) T-, The force Ftot,x is the first force Fx>ass exerted by the first control module 20 for the control of the amplitude of the vibrations according to the pilot mode at the pilot amplitude. Similarly, if we separate the terms along the y-direction of the detection mode, phase or phase opposition with position x of the mass M of the elements in quadrature with this position, by decomposing Ftot>y into:

[0153] [Math. 14] y.phti.se “1” y.qutiel

[0154] we obtain the system of equations 15:

[0155] [Math. 15] (r2cos(20) -rlsin(20) )x = Fv,,*„ (1) (-26-2Ü ')Mwx = F„atl (2)

[0156] The term FyjPhase, with amplitude FyjPhasejmax, is managed by the second control module 25 which receives the instruction to control the amplitude of the vibrations according to the detection mode at ymax = 0 and the term Fy>quad, with amplitude Fy>quadmax, is the third force imposed by the second control module 25.

[0157] Equation 15(2) shows that in order to control the rotation of the xyZ frame with respect to the XYZ frame, it is necessary to control the third force F y.quad of non-zero amplitude Fy>quad>max, in the direction y of the detection mode and in quadrature with the vibrations of the mass M along the direction x of the pilot mode.

[0158] The x and y directions of the pilot and detection modes then rotate at a frequency dO / dt different from the instantaneous angular velocity Q(t), and one can simultaneously: - reduce, or even eliminate, harmonic errors by controlling a rotation of these directions through periodic modification of the direction of the third force Fy>quad, and - deduce the instantaneous angular velocity Q(t) from the measurement of dO / dt according to equation 16:

[0159] [Math. 16].- x __ / , F

[0160] II) PROCESS OF THE PRIOR ART

[0161] In prior art processes, to obtain the third force Fy quad, the characteristics of the electrical voltage Vexc,y(t) to be applied to the electrostatic excitation device 25B are provided to the second control module 25 during a step that could be described as an initialization step. This provides, in particular, the amplitudes and angular frequencies of the different components of the voltage Vexc>y(t), which must be in quadrature phase with the position x of the mass M.

[0162] Based on the principle of equation 1, the electrical voltage Vexc>y(t) is typically of the form Vexc>y(t) = VOy + Viy sin(eut), so that the force Fy>quadth theoretically applied to the mass M is proportional to the DC component VOy of the electrical voltage Vexc>y(t) and to a geometric factor ggeom characteristic of the electrostatic excitation device 25B. In the case of prior art processes, the following is therefore theoretically controlled:

[0163] [Math. 17] (2V0vVlvsin(y))

[0164] This control step is represented by step 510 of [Fig.7], on which it is observed that the force Fy>quadthest is controlled in order to cause a rotation of the pilot mode direction in the frame of reference of the housing at a control angular velocity Qcom.

[0165] The scale factor between the controlled force Fy>quadth and the control angular velocity Qcom is constant and denoted Cl.

[0166] Due to delays and gain errors in the electronics and mechanics, including detection errors on the position of the vibrating element, errors on the voltages VOy>Viy, as well as errors on the sinusoidal signal sin ( oV ), the force F y,quadapp actually applied to the test mass M differs more or less from the commanded force F y,quadth, both in amplitude and in phase.

[0167] The difference between the amplitude Fy>quad>maxth of the commanded force and the amplitude Fy quadjmaxapp of the force actually applied can be modeled by:

[0168] [Math. 18] Fy.quadjnax= (i+4z) ) F*uaita„ = c2 Qc“\ 1+40)

[0169] where e(t) is a very unstable error term due to the many electronic and mechanical parameters that cause it and C2 denotes a constant scaling factor.

[0170] Following the control step 510, the force Fy quad“pp is actually exerted during an acquisition step 520, resulting in an effective rotation of the pilot mode direction in the housing's frame of reference at an effective angular velocity Q“pp different from the control angular velocity Qcom. These two angular velocities are related by the following equation, in which C3 denotes a constant scale factor:

[0171] Qapp

[0172] In the prior art measurement method, the measured instantaneous angular velocity is deduced from equation 16 and the amplitude Fy>quad>maxth controlled for the third force Fy>quad, which is provided during the initialization step to the second servo device 25, according to the formula:

[0173] [Math. 19]

[0174] The effective instantaneous angular velocity Q“pp, which would be deduced from equation 16 and the amplitude Fy>quad>maxapp actually obtained for the third force Fy>quad if it were perfectly known (i.e. if all the sources of error were par-

[0175]

[0176]

[0177]

[0178]

[0179]

[0180]

[0181]

[0182]

[0183]

[0184]

[0185] (actually controlled and known), is expressed as: [Math.20] ,-jipp zx ■ my zs £2 (t) = - e (t)- rfPP * y.quadjnax The error made in the prior art process regarding angular velocity therefore for expression: [Math.21] ,■ Jhes / pPP y,quàd,m £2 — W / T 2MwxffMV H ​= and / This is therefore a scaling factor error. It is understood that if the term e is not strictly constant over time, the error related to the scaling factor does not have a zero time average, even if the time average of the controlled force Fy.quad* is zero. Furthermore, the error within a reversal period is greater the larger e(t) is. Finally, even if the term e(t) were obtained by means of calibration prior to the measurement, due to the variety of causes of this error, It is not possible to assume that this calibration will remain correct in the short or long term. III) METHOD 400 ACCORDING TO THE INVENTION The method according to the invention aims to solve this technical problem, by exerting a third force Fy quadapp of amplitude better controlled than in the methods of the prior art and by using another way of estimating the angular velocity to be measured. The amplitude of the third force is therefore not provided in the form of a setpoint value that would be provided during the initialization step. In the case of the method 400 according to the invention, during the acquisition step 430, the adjustment control Tth is implemented by the adjustment control unit 26 of the second servo module 25, so that the additional force F y,phaSe,Suppapp, of intensity Tapp|xl, in phase with the position x of the mass M and in the direction y of the detection mode is effectively imposed on the mass M. The control of the amplitude of the vibrations of the mass M along the direction y of the detection mode is achieved by the second servo module 25 in the presence of the additional force Fy phasejSUpPaPP actually applied. Acquisition step 430 is shown in detail in [Fig.8]. The additional force Fy phasejSUppaPP is actually applied in a substep of application 4301. Due to the presence of the additional force, the system of equations 15 can therefore be written for the process of the invention in the form of the system of equations 22:

[0186] [Math.22] (r2cos(20) -rlsin(20) = < — F'y.phasefis.s+ 7^008(20+ tp^x (1) (-20-2fi)MUtt = X^„,^

[0187] with q> a constant value. For example, q> = 0 if quadrature combs of the tuning type are used and, for example, q> = ir / 2 if frequency combs of the tuning type are used.

[0188] The force Fy>phase>assapp which is actually exerted by the second servo device 25 in phase with the position x of the mass M to achieve the servo control of the vibrating element 15 along the direction y of the detection mode therefore has the following expression:

[0189] [Math.23] = (r2cos(20) - rIsin (20) -7^ cos(20 + (p))x

[0190] It is observed that part of the force FyjphaSejassapp intervenes to counter the additional force FyjphaSejSUppapp applied through the injection of the adjustment command Tth.

[0191] During an estimation substep 4302 of the acquisition step 430, the servo device 25 estimates the force Fv.pi^e.+J''' to be commanded to actually exert the force Fy.phase.ass^ on the vibrating element 15 for its servo control in the presence of the additional force FyjPhaSejSupPapply actually exerted by the adjustment unit 26.

[0192] The force Fy>phase!ass“pp is actually exerted during a first substep of exercise 4303, in the presence of the additional force Fy>phase>suppapp.

[0193] The difference between the force Fyphasejassflpp actually applied to exercise substep 4303 and the estimator of the force to be commanded to exert can be modeled this force, obtained at estimation substep 4302, by equation 24:

[0194] [Math.24] = ( 14- é <zBF&\ 1 y,phase,assanax \ 1 ~} / 1 y,phase,assanax

[0195] Since the term e(t) is much less than 1, we can still write, as has been done in [Fig.8]:

[0196] [Math.25] 1 y,phase,assjnax \ 1 J1 y,phase,ass,max

[0197] or again:

[0198] [Math.26] 1^«^ = (r2cos(20) -rlsin(29)-7™W20 + ) ( 1-

[0199] It should be noted that the term TaPPcos(20+q>) x is present in the force Fy phasejassflpp and in the estimator Fj^e^ / '' of process 400 (unlike prior art processes) due to the injection of the adjustment command Tth.

[0200] During an extraction substep 4304, the second control device 25 extracts from the force FyjPhase>ass thus estimated at least one estimator T;est of an amplitude Ti“pp of the harmonic decomposition of T“pp , on the basis of the spectral signature of the adjustment control Tth.

[0201] By way of non-limiting example, Tth may be chosen to be of the form:

[0202] [Math.27] Tth=T2cof&0 + v)

[0203] in which angle 0 designates the angular position of the x direction of the pilot mode with respect to the X reference axis of the XYZ frame linked to the housing 12.

[0204] In this case, the average value of the term TaPPcos(20+q>) over a period characteristic of the variations of the angle 0 is equal to T2aPP / 2, so that it is possible to extract T2app from the force estimated Fy>pi,.,,e,,by the control device 25 and to evaluate T2“pp, for example by filtering with an averaging filter.

[0205] An odd-rank harmonic can also be used. This arrangement facilitates the separation of the component of interest from the physical signals. For example, the terms T; of the spectral signature of the adjustment control Tth can be constant, or sinusoidal of the form T; = X;cos(ai t + [30 where a;, Xiet[3i are predetermined constants.

[0206] Then, during a control substep 4305, the servo device processor 25 commands the third force Fy,quad,A, in the direction y of the sensing mode but in quadrature with the additional force FyjphasejSuppth.

[0207] As can be seen in [Fig.8], the third controlled force Fy>quadth includes a term proportional to each of the estimators T;est, the scale factor being constant and denoted C4.

[0208] During a second substep of exercise 4306, the command of the third force Fy.quad* results in the exercise of the third force Fy>quadapply actually applied.

[0209] Since the errors are the same in each of the substeps, the third force Fy>quadapp actually applied is in quadrature with the additional force Fy phasejSUppaPP and it therefore ultimately includes a component proportional to each of the real harmonics T;app of T“pp used, the proportionality factor being constant and denoted C5.

[0210] Equation 16 can then be rewritten as follows, in which C6 denotes a constant scaling factor:

[0211] [Math.28] / ) _ / > ^7 _ Z) Z"1 T^PP ^mes~ 2M<<! — i

[0212] La troisième force Fy> The previously applied angular velocity therefore has the effect of imposing an additional angular velocity of rotation on the wave frame, this additional angular velocity being proportional to the amplitude T^pp used.

[0213] It is important to understand that the error made between the second estimated force F^ph^^ / 5' and the second force actually exerted Fy phasejassflpp is the same as that between the third commanded force Fy>quad,A and the third force actually exerted Fy>quadflpp, the conversion chain being the same in both cases.

[0214] Consequently, if in the preliminary calibration step 420, the predetermined angular velocity Qcaia was imposed on the housing 12 with respect to the Z axis, with the same adjustment command Tth, it is also known, the conversion chain remaining the same, that:

[0215] [Math.29] ^PP Qal ~ ' ®cal ~ ' ®cal " + ^ref

[0216] The additional angular velocity Qapp actually applied in the case of the process according to the invention is therefore exactly the reference angular velocity Qref determined in the calibration step 420, and is not affected by the errors which occur in the prior art process, as can be seen in [Fig.8].

[0217] Thus, it only remains to determine the instantaneous angular velocity Q(t) sought using the reference angular velocity Qref determined in the calibration step 420, according to equation 30:

[0218] [Math.30] ^mes ~ ~@ + Qal+ ®cal ~ + ^ref

[0219] This equation does not require at any time an explicit calculation of the amplitude of the third applied force, thanks to the calibration step 420. The scaling factor which was involved in prior art processes is therefore totally eradicated from process 400.

[0220] The only errors that affect the measurement are those related to the implementation of the adjustment control Tth, which must be as stable as possible between the calibration step 420 and the acquisition step 430.

[0221] In particular, the electrostatic device 26A makes it possible, by its configuration, to do without the measurement of the position of the mass M according to the direction of the pilot mode and therefore to generate an additional force FyjPhaSejSUppapp which is particularly stable.

[0222] To best control these errors, an electrostatic excitation device 26A is advantageously chosen whose geometry variations are as small as possible.

[0223] For the same purpose, a bias voltage source VT that is as stable as possible is advantageously chosen.

[0224] Preferably, the bias voltage source VT includes filtering means configured to eliminate variable components of the voltage at its terminals.

[0225] Advantageously, the instantaneous angular velocity Qcai of the housing 12 with respect to the Z axis is zero during the calibration step 420. This arrangement makes it possible to minimize the error on the angular velocity Qmes determined in the determination step 440, in particular from equation 24.

[0226] Advantageously, a first adjustment command Tth is provided during a first time interval tl and a second adjustment command which is the opposite of the first adjustment command Tth is provided during a second time interval t2, so that the direction (x) of the pilot mode relative to the housing rotates in a first direction during the first time interval tl and in a direction opposite to the first direction during the second time interval t2.

[0227] Thanks to this arrangement, it is possible, by suitably choosing the first time interval t1 and the second time interval t2, to cancel the scaling factor errors and to minimize the harmonic defects which taint the measurements.

[0228] Equivalently, during the control substep 4305, a first sign can be applied during a first time interval t1, so that the third controlled force Fy,quad,A has a first direction during the first time interval t1. The opposite sign can then be applied during a second time interval t2 so that the third controlled force Fy>quad,A has a direction opposite to the first direction during the second time interval t2.

[0229] In summary, the process 100 according to the invention has the following specific features.

[0230] Firstly, the rotation of the pilot mode direction is obtained by applying an angular velocity whose amplitude is proportional to the amplitude of the additional force Fyjphasesuppapp very stable, unlike the processes of the prior art.

[0231] The additional force FyjphasejSuppaPP can be obtained, in particular, by means of adjusting combs, the stability of the additional force thus depending on the stability of the voltages used and the air gaps of the adjusting combs. The stability of the additional force FyjphasejSuppaPP is therefore much better controlled than that of a force obtained by means of a conventional precession control, which is subject to all the variations of the corresponding electronics.

[0232] Secondly, the angular velocity suppressed at the output to compensate for the precession control, i.e. the third force Fy>quadapp, is directly proportional to the magnitude of the additional stable force FyjphaSejSUppapp injected at the input, and is not the angular velocity associated with an electronically injected precession control, which is intrinsically unstable.

[0233] Thirdly, by playing on the signs of the adjustment command, it is possible to choose the direction of the third force Fy>quadapp and thus cause a rotation of the pilot mode direction in a first direction for a first duration and in a second direction for a second duration.

[0234] If the first and second durations are suitably chosen, scaling factor errors can be precisely eliminated. This is not the case in prior art processes due to the instability of the scaling factor.

[0235] It should be noted that the stable force injected at the input does not reduce the performance of the gyroscopic measuring device.

Claims

Demands

1. A method (400) for gyroscopic measurement using a sensor (10) comprising a housing (12) and a vibrating element (15) capable of vibrating relative to the housing (12) in a vibration plane (xy) simultaneously along a direction (x) of a pilot mode and along a direction (y) of a detection mode different from the direction (x) of the pilot mode, the method comprising the following steps of: - initialization (410), during which a pilot amplitude (xmax), a detection amplitude (ymax), an adjustment command (Tth) with a predetermined spectral signature, and a calibration angular velocity (Qcai) are provided; - calibration (420), including: i) the control of a first vibration amplitude in forced sinusoidal regime of the vibrating element (15) along the direction (x) of the pilot mode, to the pilot amplitude (xmax), ii) simultaneously, the application of a first stable force (FyjphasejSuppaPP) on the vibrating element (15) configured so as not to disturb the measurement of the sensor (10) from the adjustment command (Tth), and the control of a second vibration amplitude of the vibrating element (15) along the direction (y) of the detection mode to the detection amplitude (ymax), iii) simultaneously, the exercise of a second force (Fy,quadapp) on the vibrating element (15), following the direction (y) of the detection mode and in quadrature phase with the first force, the second force (Fy>quad app) being determined on the basis of a third force (FyphaSejassest) which estimates the force actually exerted to control the second amplitude and the spectral signature of the adjustment command (Tth) and configured to cause a rotation of the direction (x) of the pilot mode relative to the housing (12), an instantaneous angular velocity (Q(t)) of the housing (12) with respect to a sensitive axis (Z) being imposed and equal to the calibration angular velocity (Qcai) during i), ii) and iii); iv) the determination of a reference angular velocity (Qref) from the calibration angular velocity (Qcai) and measurements of the vibrations of the vibrating element (15) during iii); - acquisition (430), including i), ii) iii) of the calibration (420) with a free instantaneous angular velocity (Q(t)); - determination (440) of an instantaneous measured angular velocity (Qmes (t)) of the housing (12) with respect to the sensitive axis (Z) from measurements of the vibrations of the vibrating element (15) during the acquisition (430) and of the reference angular velocity (Qref).

2. Method (400) of gyroscopic measurement according to claim 1, wherein for calibration (420), the first force (FyjphasejSuppaPP) is exerted on the vibrating element (15), along the direction (y) of the detection mode and in phase with the vibrations of the vibrating element (15) along the direction (x) of the pilot mode.

3. A method according to any one of the preceding claims, wherein the calibration angular velocity (Qcai) is zero.

4. A method according to any one of the preceding claims, wherein the detection amplitude (ymax) is zero.

5. A method according to any one of the preceding claims, wherein the determination of the second force during calibration (420) and during acquisition (430) includes a filtering of the third force (FyjPhase>asset) which estimates the force actually exerted to control the second amplitude.

6. A method according to any one of the preceding claims, wherein the first force (FyjphaSe,Suppapp) is exerted by means of an electrostatic device (26A) configured to exert a force directly proportional to a position of the vibrating element along the direction (x) of the pilot mode and function of the adjustment control (Tth).

7. A method according to any one of the preceding claims, wherein the adjustment command (Tth) is of the form: Tth = To + T^osC^) + 7?cos(20 + ... + Tncos(M) where n is a strictly positive integer, T; for i an integer between 1 and n denotes a constant term and 0 denotes an angular position of the direction (x) of the pilot mode with respect to a reference axis (X) of a frame (XYZ) linked to the housing, the reference axis (X) being orthogonal to the sensitive axis (Z).

8. A method according to any one of the preceding claims, wherein a first adjustment command (Tth) is provided during a first time interval (t1) and a second adjustment command, which is the opposite of the first adjustment command, is provided during a second time interval (t2), such that the direction (x) of the pilot mode relative to the case rotates in one direction during the first time interval and in the opposite direction to the first direction during the second time interval.

9. Gyroscopic sensor comprising: - a case (12); - a vibrating element (15) capable of vibrating relative to the housing (12) in a vibration plane (xy) simultaneously along a direction (x) of a pilot mode and along a direction (y) of a detection mode different from the direction (x) of the pilot mode; - a first servo module (20), configured to receive a pilot amplitude (xmax) and to servo to a predetermined pilot amplitude (xmax) a first vibration amplitude in forced sinusoidal regime of the vibrating element (15) along the direction (x) of the pilot mode; - a second servo module (25) configured for: a) exert on the vibrating element (15) a first stable force (Fy,phaSe,Supp app) configured so as not to disturb the measurement of the sensor (10) from an adjustment command (Tth) whose spectral signature is predetermined, b) to control a second vibration amplitude of the vibrating element (15) along the direction (y) of the detection mode, based on a predetermined detection amplitude (ymax), and c) exert a second force (Fy>quadapp) on the vibrating element (15), along the direction (y) of the sensing mode and in quadrature phase with the first force, the second force (Fy>quadapp) being configured to cause a rotation of the direction (x) of the pilot mode relative to the housing (12), the second force (Fy>quadapp) being determined on the basis of a third force (FyjPhaseassest) which is an estimate of the force actually exerted to control the second amplitude and of the spectral signature of the adjustment control (Tth); - a measurement module (30) configured to generate vibration measurements of the vibrating element (15) along the x directions of the pilot mode and y directions of the detection mode and to exchange information with the first servo module (20) and with the second servo module (25); - a determination module (35) configured to exchange information with the measurement module (30) and the first and second control modules (20, 25) and to determine: i) a reference angular velocity (Qref) from a velocity predetermined angular calibration velocity (Qcai) and from vibration measurements of the vibrating element 15 transmitted by the measuring module (30) in a calibration mode for which an instantaneous angular velocity (Q(t)) of the housing (12) with respect to a sensitive axis (Z) is imposed and equal to the angular calibration velocity (Qcai), and ii) an instantaneous angular velocity measured (Qmes(t)) of the housing (12) with respect to the sensitive axis (Z) from measurements of the vibrations of the vibrating element (15) in an acquisition mode in which the instantaneous angular velocity (Q(t)) is free and from the reference angular velocity (Qref).

10. Gyroscopic sensor according to the preceding claim, wherein the first servo module (20) and the second servo module (25) comprise electrostatic excitation means (20A, 25A).

11. Computer program comprising instructions that cause the sensor (10) according to claim 9 or claim 10 to perform the method (400) according to any one of claims 1 to 8.

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