Gyroscopic measuring 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 command (Tth) of predetermined spectral signature, and a calibration angular velocity (Ωcal);a calibration (420), comprising the control of the pilot amplitude and the detection amplitude of the vibrations of the vibrating element (15) in 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 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 speed (Ω(t)) of the housing (12) being imposed equal to the calibration angular speed (Ωcal), and the determination of a reference angular speed (Ωref); an acquisition (430), similar to the calibration but with a free instantaneous angular speed (Ω(t)); a determination (440) of a measured instantaneous angular velocity (Ωmes(t)). Figure for the abstract: 3;

Description

Title of the invention: Gyroscopic measuring 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 which cause the sensor to execute the step of determining the instantaneous angular velocity of the gyroscopic sensor of this method.

[0003] A Coriolis Vibratory Gyroscope (CVG) sensor makes it possible to measure the component along an axis, called the sensitivity axis, of an instantaneous rotation speed vector of a reference frame linked to a sensor housing relative 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 which is exerted on the vibrating element.

[0005] The vibrating element of a CVG is capable of vibrating in 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 pilot mode and detection mode directions.

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

[0008] If the component along the sensitivity axis of the instantaneous rotation speed vector of the housing relative to an inertial reference frame is non-zero, the displacement of the vibrating element along the direction of the pilot mode generates a Coriolis force. This force excites the vibrating element along the direction of the detection mode, at an amplitude which is proportional to the component along the sensitivity axis of the instantaneous rotation speed vector.

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

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

[0011] In gyrometer mode, the direction of the pilot mode in the vibration plane 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 in gyrometer mode, the measurements are affected by intrinsic errors linked to defects in the CVG. Among these defects, we can cite anisotropies of stiffness or damping of the vibrating element, defects in the excitation control electronics or in the electronics for detecting the position of the vibrating element, defects in the reference electrical 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 frame of reference linked to the box.

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

[0015] US 7,093,370 further describes a MEMS gyrometer in which an angular velocity is deliberately 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 errors in the scale factors of the gyrometer.

[0016] FR 2937414 describes a vibrating gyroscope which combines the principles of US patents 6,598,455 by injecting an electronic signal to rotate the vibration wave and US 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 a first direction during a portion of the period of the control signal according to a first speed profile, then in an opposite direction according to a second speed profile. The vibrating gyroscope then provides a corrected signal which is based on the difference between the measurement signal and the control signal.

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

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

[0019] However, this is very unlikely, because the sources of errors are numerous and of different natures. We can notably cite 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 cards which coordinate the implementation of the gyroscopic measurement process.

[0020] Ultimately, in most situations, the average value of the error made is not zero over a period of the alternating rotation of the position of the sensor. Furthermore, during the round trip of the wave, the angular errors of the sensor are all the greater as the defects mentioned above are significant.

[0021] Such a device reduces the impact of defects on the measurement without, however, making it possible to evaluate the measurement error linked to these defects.

[0022] Furthermore, the control signal used in FR 2937414 must make it possible to return to the same angular position between the start and the 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 make it possible to have a zero-mean control signal and to return to the same angular position at the same time.

[0023] An aim 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 the measurement errors, in particular the scale factor error, are reduced.

[0024] To this end, the invention relates to a method of gyroscopic measurement by means of a sensor comprising a housing and a vibrating element capable of vibrating relative to the housing in a vibration plane simultaneously in a direction of a pilot mode and in a direction of a detection mode different from the direction of the pilot mode, the method comprising the following steps of: - 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 to the pilot amplitude of a first amplitude of vibrations in forced sinusoidal mode of the vibrating element in the direction (x) of the pilot mode, ii) simultaneously, the exertion of a first stable force on the vibrating element configured so as not to disturb the measurement of the sensor from the adjustment command, and the control to the detection amplitude of a second amplitude of vibrations of the vibrating element following the direction of the detection mode; iii) simultaneously, exerting a second force on the vibrating element, following the direction of the detection mode and in phase quadrature with the first force, the second force being determined on the basis of a third force which estimates the force actually exerted 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 relative to a sensitive axis being imposed and equal to the calibration angular velocity during i), ii) and iii); iv) determining a reference angular velocity from the calibration angular velocity and measurements of the vibrations of the vibrating element during iii); - acquisition, including i), ii) iii) of calibration with a free instantaneous angular velocity; - determination of an instantaneous angular velocity measured by the housing relative 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 command is used to apply to the vibrating element a first force in the direction of the detection mode, in phase with the vibrations in 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 made 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 good stability of the second force.

[0030] The second force is, as in the prior art, controlled to cause an additional rotation of the pilot mode and detection mode directions, in addition to the rotation related to the Coriolis force in order to reduce 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, thanks to the particular and stable method of obtaining the second force.

[0032] Unlike patent FR 2937414, the measurement is deduced from the measurement signal not by removing an injected signal which is supposed to reconstitute a precession force but by removing a precession command which results from the projection of a force obtained through the servocontrols, this force being implemented to counter the injection of a very stable force voluntarily injected onto the sensor. In other words, to obtain the angular velocity at the output, an unstable controlled signal is not subtracted from the measurement but the image of a very stable force by design.

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

[0034] According to an advantageous aspect of the invention, the calibration comprises: i) the control of the pilot amplitude of a first amplitude of vibrations in forced sinusoidal mode of the vibrating element in the direction of the pilot mode, ii) simultaneously, exerting a first force on the vibrating element, in the direction of the detection mode and in phase with the vibrations of the vibrating element in the direction of the pilot mode, from the adjustment command and controlling the detection amplitude of a second amplitude of vibrations of the vibrating element in the direction of the detection mode, iii) simultaneously, exerting a second force on the vibrating element, following the direction of the detection mode and in phase quadrature with the first force, the second force being determined on the basis of a third force which estimates the force actually exerted to control the second amplitude and the spectral signature of the adjustment command and configured to cause a rotation of the direction of the pilot mode 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 characteristics, taken in isolation or in all technically possible combinations:

[0036] - for calibration, the first force is exerted on the vibrating element, following 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 force actually 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 a function of the adjustment command;

[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 integer between 1 and n denotes a constant term and 0 denotes an angular position of the direction of the pilot mode 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 that is the opposite of the first adjustment command is provided during a second time interval, such that the direction of the pilot mode relative to the housing rotates in a first direction during the first time interval and in a direction opposite to the first direction 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 vibration plane simultaneously in a direction of a pilot mode and in 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 to a predetermined pilot amplitude a first amplitude of vibrations in forced sinusoidal mode of the vibrating element in the direction of the pilot mode; - a second servo module configured for: a) exerting on the vibrating element a first stable force configured so as not to disturb the measurement of the sensor from an adjustment command whose spectral signature is predetermined, b) slaving a second amplitude of vibrations of the vibrating element in the direction of the detection mode to a predetermined detection amplitude, and c) exerting a second force on the vibrating element, along the direction of the detection mode and in phase quadrature 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 command; - a measurement module configured to generate measurements of the vibrations of the vibrating element along the x directions of the pilot mode and y directions 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 servo modules and to determine: i) a reference angular velocity from a calibration angular velocity predetermined and from measurements of the vibrations of the vibrating element 15 transmitted by the measuring module in a calibration mode for which an instantaneous angular speed of the housing relative to a sensitive axis is imposed and equal to the calibration angular speed, and ii) a measured instantaneous angular velocity of the housing relative 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 comprise electrostatic excitation means.

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

[0046] The invention will appear more clearly on reading the description which follows, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0047] [Fig-1] [Fig.l] 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 prior art.

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

[0050] [Fig.4] [Fig.4] is a schematic representation of the trajectory of the element vibrating from [Fig.l] and the directions of its pilot and detection modes in a space 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 [Fig.2];

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

[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 produced in the form of a microelectromechanical system (in English "Micro Electromechanical Sensor", MEMS). The vibrating element 15 and the housing 12 are then cut from a block of silicon or quartz by micro-machining and the vibrating element 15 is vibrated by an electrical process. This arrangement makes it possible to minimize the size and / or the manufacturing cost of the CVG 10.

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

[0059] The CVG 10 is configured to measure an instantaneous angular velocity Q(t) of the sensor relative 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 in two directions x and y, with a specific pulsation 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 visible in [Fig.4], the angular position of the x direction of the pilot mode is identified by the angle 0 defined relative to the reference axis X of the space reference (XYZ) linked to the housing 12.

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

[0064] The CVG 10 comprises a first servo-control module 20 capable of servo-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 a sinusoidal regime forced to 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 servo module 20 comprises usual means for servo-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. These are, for example, the servo-control means described in the document EP2960625.

[0066] As an example, which will be called a reference example hereinafter, the first servo module 20 comprises 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, for example, a set of interdigitated combs, as shown in [Fig. 6]. The first amplitude command 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 depending on 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 is, after filtering the pulsation terms 2co, 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 in the following, 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 an appropriate 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 pulsation force Fx>ass substantially equal to the own 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 comprises 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 the programmable logic circuit is advantageously configured to manage the control of the pulsation of the vibrations of the vibrating element 15 according to the direction x of the pilot mode, for example to the resonance pulsation co.

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

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

[0077] Thus, in the reference example, the second servo module 25 comprises 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, 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 command, on the principle described for the first servo module 20.

[0078] The second servo module 25 comprises 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 second amplitude command. The second servo module 25 also comprises a proximity card, configured to inject the second amplitude command signal into the electrostatic device 25A.

[0079] The processor or programmable logic circuit is in the reference example the same as that of the first servo module 20. This arrangement is advantageous without being obligatory.

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

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

[0082] The second servo module 25 comprises 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 direction y of the detection mode, in phase with the vibrations of the vibrating element 15 in the direction x of the pilot mode.

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

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

[0085] For this purpose, the adjustment control unit 26 may comprise 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 proof mass M in the direction of the pilot mode.

[0086] Typically, the electrostatic device 26A is a trimming comb polarized by a very stable polarization voltage VT and which is capable of exerting a force in the direction of the detection mode, directly proportional to the position x of the proof mass M in the direction of the pilot mode and proportional to the square of the polarization 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 equation (b) below, in which K denotes a gain which 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 will be noted that the physical principle is entirely different from a force Faa which would be obtained, as in the devices of the prior art, by means of an excitation comb following the direction of the pilot mode, which would be given by the 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, i.e. a comb involves a coupling between the pilot mode and the detection mode.

[0094] Alternatively, the adjustment comb is a frequency adjustment comb, i.e. a physical device configured to modify at least one of the natural pulsations of the proof 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 direction y of the detection mode is carried out 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 phase quadrature with the additional force FyphasejSUppaPP, on the basis of a spectral signature of the adjustment command Tth and an estimation 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 in 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 relative to the sensitive axis Z of the sensor 10 in the inertial frame of reference is imposed, of value equal to a predetermined calibration angular velocity Qcai, and - a second case, for which the instantaneous angular velocity Q(t) is free to establish itself under the effect of the movement of the housing 12, in particular linked to the movement of a device on which the CVG 10 is implemented, and during which the instantaneous angular velocity Q(t) is therefore unknown a priori, and to be determined. In this second case, the instantaneous angular velocity is therefore not imposed, in particular at 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, with a view to servo-controlling the vibrations of the vibrating element 15.

[0098] The measurement module 30 is capable of generating measurements of the vibrations of the vibrating element 15 along the directions x of the pilot mode and y of the detection mode and 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 speed dx / dt(t) (respectively dy / dt(t)) and / or its acceleration d2x / dt2(t) (respectively d2y / dt2(t)) along the x direction (respectively along the y direction).

[0100] To this end, the measurement module 30 comprises, 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 shown 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 to 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 servo 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 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 a measured instantaneous 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 speed Qref.

[0107] The method 400 according to the invention will now be described with reference to FIGS. 3, 5 and 8, in comparison with the method of the prior art shown in FIGS. 2 and 7.

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

[0109] The initialization step 410 comprises: a) supplying to the first servo module 20 the non-zero pilot amplitude xmax to which the characteristic amplitude of the vibrations in forced sinusoidal mode of the vibrating element 15 in the direction x of the pilot mode must be controlled, b) supplying to the second servo module 25 the detection amplitude ymax to which the characteristic amplitude of the vibrations of the vibrating element 15 in the direction y of the detection mode must be controlled, c) providing the adjustment control unit 26 with the adjustment command Tth, the spectral signature of which is known, and d) supplying the calibration angular velocity ^cal* to the determination module 35

[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 mode along the direction x of the pilot mode is controlled by 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 direction x of the pilot mode from the measurement module 30. ii) simultaneously, the additional force FyjphasejSuppaPP, the direction of which is the y direction of the detection mode and in phase with the vibrations of the vibrating element 15 in the x direction, is exerted by the adjustment unit 26 from the adjustment command Tth and the characteristic amplitude of the vibrations of the vibrating element 15 in 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 in the y direction of the detection mode and in 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 phase quadrature with the additional force FyjPhaSejSupPapp, on the basis of an es Timation FyjPhase assest of the second force Fy>phase>assapp actually exerted by the second servo device 25 to servo the characteristic amplitude of the vibrations of the vibrating element 15 in the direction y 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 directions x, y of the pilot and detection modes relative to the housing 12. iv) the second servo module 25 controls the exertion 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 mode along the x direction of the pilot mode is slaved to the non-zero pilot amplitude xmax by means of the first servo module 20, and the characteristic amplitude of the vibrations of the vibrating element 15 along the y direction is slaved to the detection amplitude ymax in the presence of the additional force Fy phase suppapp 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 servo 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 exerted by means of a device making it possible to obtain a stable amplitude. In addition, the additional force is configured so as not to disturb the measurement carried out by the sensor.

[0114] More generally, the additional force is exerted by means of a device making it possible to obtain 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] In addition, the additional force is configured so as not to disturb the measurement made 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 relative 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] At the end of the acquisition step 430, the determination step 440 is implemented by means of the determination module 35: the determination module 35 determines the measured instantaneous angular velocity Qmes(t), which is an estimator of the instantaneous angular velocity Q(t) of the housing 12, from the measurements of the vibrations of the vibrating element 15 transmitted by the measurement module 30 to the first and second servo modules 20, 25 during the acquisition step 430 and from the reference angular velocity Qref determined in the calibration step 420.

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

[0119] To simplify the writing of the equations making it possible to understand the method of the prior art and the method 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.l].

[0120] Furthermore, it is considered in the following that the stiffness constants and the natural pulsations of the vibrating element 15 are identical according to the pilot mode x and the mode y. In this particular case, it can therefore be written that Kx= Ky= K and that cüox = co0y = coq.

[0121] This simplification should in no case be considered as limiting for 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] Generally speaking, the trajectory of the mass M in forced sinusoidal mode 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 following the detection mode is controlled by a zero detection amplitude ymax.

[0124] Without making any assumption at this stage on 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 date 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 date t is of the form y(t) = ymaxsin (eut).

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

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

[0127] in which R(0) is the transition 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 METHOD AND TO THE METHOD 400 ACCORDING TO THE INVENTION In the prior art method shown in [Fig. 2], as in the method 400 according to the invention, the passage matrix R(0) is a function of time. Indeed, in these methods a rotation of the xyZ reference frame relative to the XYZ reference frame is controlled, therefore a temporal evolution of the angle 0, with the aim of eliminating the harmonic errors of the CVG 10. Furthermore, in gyroscope mode, the angle 0 is free to evolve and the servocontrols are carried out in the xyZ reference frame. The first time derivatives dX / dt and dY / dt of the X and Y coordinates of the mass M therefore verify: [Math.4] [ Y] = 0 ■ ' LyJ \ The second time derivatives d2X / dt2 and d2Y / dt2 of the X and Y coordinates of the mass M verify: [Math.5] ["XL x-32x-23y-3y W \ fl2ÔX+ëx+y-è\ In a forced sinusoidal regime at the co pulsation, if we neglect the terms which are not proportional to a positive integer power of the co pulsation in front of 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 box 12, the mass M is subjected to the forces FtotjX and Ftot>y exerted respectively by the excitation devices 20A, 25A, to the return forces of the springs, as well as to 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 animated by a rotational movement of component Q(t) in the direction Z relative to the inertial frame of reference, the mass M, due to its non-zero relative speed in the frame of reference of the housing 12, is subjected to a Coriolis inertial force in this frame of reference of the box 12.

[0140]

[0141]

[0142]

[0143]

[0144]

[0145]

[0146]

[0147]

[0148]

[0149]

[0150]

[0151]

[0152] Newton's second law applied to the mass M in the non-Galilean frame of reference of the box allows us to obtain equation 9: [Math.9] + a[^1 +2Q LYJ 'L Kl y To simplify the writing of the equations, the damping anisotropies are neglected in the following, without this being limiting for the implementation of the process. Neglecting damping anisotropies, equation 9, after multiplication by R(-0) and with the approximations of equation 5, is written as follows: [Math. 10] In the case where the amplitude ymax of the vibrations following the detection mode is controlled by 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 phase opposition 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,phaxe + Fx,quad we obtain the system of equations 13: [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 servo module 20 for the servo-control of the vibration amplitude according to the pilot mode to the pilot amplitude. Similarly, if we separate along the y direction of the detection mode the terms in phase or phase opposition with the position x of the mass M of terms 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, of amplitude FyjPhasejmax, is managed by the second servo module 25 which receives the instruction to servo the amplitude of the vibrations according to the detection mode at ymax = 0 and the term Fy>quad, of amplitude Fy>quadmax, is the third force imposed by the second servo module 25.

[0157] We find with equation 15(2) the fact that to control the rotation of the xyZ frame relative 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 pulsation dO / dt different from the instantaneous angular velocity Q(t) and we can both: - reduce, or even eliminate, harmonic errors, by controlling a rotation of these directions by 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 the methods of the prior art, to obtain the third force Fy quad, the second servo module 25 is provided with the characteristics of the electrical voltage V exc,y(t) which is to be applied to the electrostatic excitation device 25B during a step which could be described as an initialization step. In particular, the amplitudes and the pulsations of the different components of the voltage Vexc>y(t) are thus provided, which must be in phase quadrature with the position x of the mass M.

[0162] On the principle of equation 1, the electric 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 continuous component VOy of the electric voltage Vexc>y(t) and to a geometric factor ggeom characteristic of the electrostatic excitation device 25B. In the case of the methods of the prior art, we therefore theoretically control:

[0163] [Math. 17] (2V0vVlvsin («y))

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

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

[0166] Due to delays and gain errors in the electronics and mechanics, including detection errors in the position of the vibrating element, errors in the voltages VOy>Viy, as well as errors in 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 scale factor.

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

[0171] Qapp

[0172] In the measurement method of the prior art, the measured instantaneous angular velocity is deduced from equation 16 and from the amplitude Fy>quad>maxth commanded for the third force Fy>quad, which is supplied 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 errors were par-

[0175]

[0176]

[0177]

[0178]

[0179]

[0180]

[0181]

[0182]

[0183]

[0184]

[0185] fully controlled and known), has the expression: [Math.20] ,-jipp zx ■ my zs £2 (t) = - e (t)- rfPP * y.quadjnax The error made in the prior art method on the angular velocity has therefore for expression: [Math.21] ,■ Jhes / pPP y,quàd,m £2 — W / T 2MwxffMV H ​= and / This is therefore a scale factor type error. We understand that if the term e is not strictly constant over time, the error linked to the scale factor does not have a zero time average even if the time average of the commanded force Fy.quad* is zero. In addition, the error within a reversal period is all the greater as e(t) is large. Finally, even if the term e(t) was obtained by means of a calibration upstream of the measurement, due to the variety of causes of this error, it is not possible to consider that this calibration will remain correct in the more or less 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 better controlled amplitude than in the methods of the prior art and by using another way of estimating the angular speed to be measured. The amplitude of the third force is therefore not provided in the form of a setpoint value which 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 command 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 of direction the direction y of the detection mode is effectively imposed on the mass M. The servo-control of the amplitude of the vibrations of the mass M along the direction y of the detection mode is carried out by the second servo module 25 in the presence of the additional force Fy phasejSUpPaPP actually applied. The acquisition step 430 is shown in detail in [Fig.8]. The additional force Fy phasejSUppaPP is actually applied in an application substep 4301. Due to the presence of the additional force, the system of equations 15 can therefore be written for the method 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 adjusting combs of the quadrature comb type are used and, for example, q> = ir / 2 if adjusting combs of the frequency comb 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 according to 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 sub-step 4302 of the acquisition step 430, the servo-control device 25 estimates the force Fv.pi^e.+J''' to be controlled to actually exert the force Fy.phase.ass^ on the vibrating element 15 for its servo-control in the presence of the additional force FyjPhaSejSupP actually exerted by the adjustment unit 26.

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

[0193] We can model the difference between the force Fyphasejassflpp actually applied to the exercise sub-step 4303 and the estimator of the force to be commanded to exercise this force, obtained in estimation sub-step 4302, by equation 24:

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

[0195] The term e(t) being much less than 1, we can still write, as was 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] Note that the term TaPPcos(20+q>) x is present in the force Fy phasejassflpp and in the estimator Fj^e^ / '' of the method 400 (unlike the methods of the prior art) due to the injection of the adjustment command Tth.

[0200] During an extraction sub-step 4304, the second servo-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 command Tth.

[0201] As a non-limiting example, we can choose Tth of the form:

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

[0203] in which the angle 0 designates the angular position of the direction x of the pilot mode relative to the reference axis X of the XYZ reference 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 estimated force Fy>pi,.,,e,, by the servo-control device 25 and to evaluate T2“pp, for example by filtering with an averaging filter.

[0205] An odd-order 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 command Tth can be constant, or sinusoidal of the form T; = X;cos(ai t + [30 where a;, Xi and [3i are predetermined constants.

[0206] Then, during a control sub-step 4305, the processor of the servo device 25 controls the third force Fy,quad,A, in the direction y of the detection mode but in quadrature with the additional force FyjphasejSuppth.

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

[0208] During a second exercise sub-step 4306, the command of the third force Fy.quad* results in the exercise of the third force Fy>quadactually applied.

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

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

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

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

[0213] It is important to understand that the error 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 speed Qcai was imposed on the housing 12 with respect to the Z axis, with the same adjustment command Tth, we also know, 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 method 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 method of the prior art, as can be seen in [Fig.8].

[0217] Thus, all that remains is 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 force applied, thanks to the calibration step 420. The scale factor which intervened in the methods of the prior art is therefore totally eradicated from the method 400.

[0220] The only errors that affect the measurement are those linked to the implementation of the Tth adjustment command, 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 measuring the position of the mass M in the direction of the pilot mode and therefore to generate a particularly stable additional force FyjPhaSejSUppapp.

[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 is advantageously chosen to be as stable as possible.

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

[0225] Advantageously, the instantaneous angular speed Qcai of the housing 12 relative to the Z axis is zero during the calibration step 420. This arrangement makes it possible to minimize the error on the angular speed 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 scale factor errors and to minimize the harmonic defects affecting the measurements.

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

[0229] In summary, the method 100 according to the invention has the following specificities.

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

[0231] The additional force FyjphasejSuppaPP can in particular be obtained by means of adjustment combs, the stability of the additional force therefore depending on the stability of the voltages used and the air gaps of the adjustment 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] Second, the angular velocity suppressed at the output to compensate for the precession command, 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, intrinsically unstable, precession command.

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

[0234] If the first duration and the second duration are properly chosen, the scale factor errors can be eliminated precisely. This is not the case in the prior art methods due to the instability of the scale factor.

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

Claims

Claims

1. Method (400) of gyroscopic measurement by means of 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 in a direction (x) of a pilot mode and in 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) of which a spectral signature is predetermined, and a calibration angular speed (Qcai) are provided; - calibration (420), including: i) the control to the pilot amplitude (xmax) of a first amplitude of vibrations in forced sinusoidal mode of the vibrating element (15) in the direction (x) of the pilot mode, ii) simultaneously, the exertion 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 to the detection amplitude (ymax) of a second amplitude of vibrations of the vibrating element (15) following the direction (y) of the detection mode, iii) simultaneously, the exertion of a second force (Fy,quadapp) on the vibrating element (15), along the direction (y) of the detection mode and in phase quadrature 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) relative to a sensitive axis (Z) being imposed and equal to the calibration angular velocity (Qcai) during i), ii) and iii); iv) determining 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), comprising i), ii) iii) of the calibration (420) with a free instantaneous angular velocity (Q(t)); - determination (440) of a measured instantaneous angular velocity (Qmes (t)) of the housing (12) relative 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 the calibration (420), the first force (FyjphasejSuppaPP) is exerted on the vibrating element (15), in the direction (y) of the detection mode and in phase with the vibrations of the vibrating element (15) in the direction (x) of the pilot mode.

3. Method according to any one of the preceding claims, in which the calibration angular velocity (Qcai) is zero.

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

5. Method according to any one of the preceding claims, in which the determination of the second force during the calibration (420) and during the acquisition (430) comprises a filtering of the third force (FyjPhase>assest) which estimates the force actually exerted to control the second amplitude.

6. Method according to any one of the preceding claims, in which 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 according to the direction (x) of the pilot mode and depending on the adjustment command (Tth).

7. Method according to any one of the preceding claims, in which 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 integer between 1 and n denotes a constant term and 0 denotes an angular position of the direction (x) of the pilot mode relative to a reference axis (X) of a reference frame (XYZ) linked to the housing, the reference axis (X) being orthogonal to the sensitive axis (Z).

8. A method according to any preceding claim, wherein 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 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 and in a direction opposite to the first direction during the second time interval.

9. A gyroscopic sensor comprising: - a housing (12); - a vibrating element (15) capable of vibrating relative to the housing (12) in a vibration plane (xy) simultaneously in a direction (x) of a pilot mode and in 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 amplitude of vibrations in forced sinusoidal mode of the vibrating element (15) in the direction (x) of the pilot mode; - a second servo module (25) configured to: a) exerting 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) controlling a second vibration amplitude of the vibrating element (15) in the direction (y) of the detection mode to a predetermined detection amplitude (ymax), and c) exerting a second force (Fy>quadapp) on the vibrating element (15), along the direction (y) of the detection mode and in phase quadrature 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 command (Tth); - a measurement module (30) configured to generate measurements of the vibrations of the vibrating element (15) along the directions x of the pilot mode and y 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 servo modules (20, 25) and to determine: i) a reference angular velocity (Qref) from a velocity predetermined angular calibration speed (Qcai) and from measurements of the vibrations of the vibrating element 15 transmitted by the measuring module (30) in a calibration mode for which an instantaneous angular speed (Q(t)) of the housing (12) relative to a sensitive axis (Z) is imposed and equal to the angular calibration speed (Qcai), and ii) a measured instantaneous angular velocity (Qmes(t)) of the housing (12) relative 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, in which the first servo module (20) and the second servo module (25) comprise electrostatic excitation means (20A, 25A).

11. A computer program comprising instructions which cause the sensor (10) according to claim 9 or claim 10 to carry out the method (400) according to any one of claims 1 to 8.

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