Gyroscopic measurement method and sensor

Abstract

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), in order to provide a drive amplitude (xmax), a detection amplitude (ymax), an adjustment control (Tth) with a predetermined spectral signature, and a calibration angular velocity (Ωcal); a calibration (420), comprising servo-control of the vibrations of the vibrating element (15), in the direction (x) of the drive mode and in the direction (y) of the detection mode, to the drive amplitude and to the detection amplitude, and simultaneously application of a first stable force ((Fy,phase,supp app) configured so as not to disturb the measurement by the sensor (10) based on the adjustment control (Tth), and application of a second force (Fy,quad app) determined on the basis of the spectral signature of the adjustment control in order to rotate the direction of the drive mode, an instantaneous angular velocity (Ω(t)) of the housing (12) being set equal to the calibration angular velocity (Ωcal), and determination of a reference angular velocity (Ωref); an acquisition (430), which is similar to the calibration but with a free instantaneous angular velocity (Ω(t)); and determination (440) of a measured instantaneous angular velocity (Ωmes(t)).

Description

[0001]TITLE: Gyroscopic measurement method and sensor The present invention relates to a gyroscopic measurement method. 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. A Coriolis Vibratory Gyroscope (CVG) gyroscopic sensor makes it possible to measure the component along an axis, called the sensitivity axis, of an instantaneous rotation velocity vector of a reference frame linked to a housing of the sensor with respect to an inertial reference frame. The CVG comprises for this purpose a vibrating element of the sensor,able to vibrate relative to the housing. The measurement is carried out using the effects of the Coriolis inertial force exerted on the vibrating element. The vibrating element of a CVG is able to vibrate 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. The sensitivity axis of the CVG is orthogonal to the plane of the pilot mode and detection mode directions. For the measurements, the vibrating element is excited in the pilot mode direction at its resonant 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 resonant frequency, particularly related to variations in the temperature of the vibrating element,are monitored by means of a frequency control system. If the component along the sensitivity axis of the instantaneous rotational speed vector of the housing relative 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, at an amplitude which is proportional to the component along the sensitivity axis of the instantaneous rotational speed vector. A CVG can operate in two modes: gyroscope mode and gyrometer mode. 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 linked to the housing. 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. 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 the 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. Among these errors,some are called harmonics because they are proportional to cosine or sine functions of an even multiple angle of the angle characterizing the direction of the pilot mode in the reference frame linked to the housing. US 6598455 describes a gyroscopic measurement method 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. US 7 093370 also describes a MEMS gyrometer in which an angular velocity is voluntarily 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. FR 2937414 describes a vibrating gyroscope which combines the principles of patents US 6598455 by injecting an electronic signal to rotate the vibration wave and US 7 093370 by imposing a periodically alternating electrical rotation making it possible to minimize harmonic errors. The control signal is adapted to rotate the geometric vibration position of the gyroscope in a first direction during part 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. However, due to the errors which affect 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 that should theoretically be obtained from the control signal. If the errors in the conversion chain are perfectly stable over time, the error made on the angle measurement may be zero over a period characteristic of the variations in the control signal. However, this is very unlikely, because the sources of error are numerous and of different natures. These include detection errors of the detection combs, excitation errors of the excitation combs as well as instabilities of the reference voltage used for the operation of these combs, and errors in the electronic cards that coordinate the implementation of the gyroscopic measurement process. Ultimately, in most situations,the average value of the error committed 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. Such a device reduces the impact of the defects on the measurement without, however, making it possible to evaluate the measurement error linked to these defects. In addition, 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 allow to have at the same time a zero-mean control signal and to return to the same angular position. 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. To this end, the subject of the invention is a gyroscopic measurement method 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 are provided, the spectral signature of which is predetermined,and a calibration angular speed; - calibration, comprising: i) the control of a first amplitude of vibrations in forced sinusoidal mode of the vibrating element in the direction (x) of the pilot mode to the pilot amplitude, ii) simultaneously, the exertion of a first force on the vibrating element configured so as not to disturb the measurement of the sensor from the adjustment command, and the control of a second amplitude of vibrations of the vibrating element in the direction of the detection mode to the detection amplitude; iii) simultaneously, the exertion of a second force on the vibrating element, in 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); iv) determining a reference angular velocity from the calibration angular velocity and measurements of the vibrations of the vibrating element during iii); - acquisition, comprising i), ii) iii) of the calibration with a free instantaneous angular velocity; - determining a measured instantaneous angular velocity of the housing relative to the sensitive axis from measurements of the vibrations of the vibrating element during the acquisition and the reference angular velocity. 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. The control of the amplitude of the vibrations in the detection mode is done in the presence of the first force and allows the second determination module to implicitly estimate the first force. The first force is configured so as not to disturb the measurement carried out by the sensor. In particular, the first force is stable, that is to say in particular produced in such a way that its amplitude is particularly stable. A second force is then exerted from this estimator, in quadrature with the first force in the direction of the detection mode of the sensor. This method of obtaining the second force allows good stability of the second force. The second force is, as in the prior art,commanded to cause an additional rotation of the pilot mode and detection mode directions, in addition to the rotation linked to the Coriolis force in order to reduce harmonic errors of the sensor. 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. 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. The measurement errors, in particular the error linked to the scale factor, are therefore reduced. 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, the exertion of 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 the control of the detection amplitude of a second amplitude of vibrations of the vibrating element along the direction of the detection mode, iii) simultaneously, the exertion of 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 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 comprises i), ii) iii) of the calibration with a free instantaneous angular velocity. According to other advantageous aspects of the invention,the gyroscopic measuring method comprises one or more of the following characteristics, taken individually or in all technically possible combinations: - 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; - the calibration angular velocity is zero; - the detection amplitude is zero; - the determination of the second force during the calibration and during the acquisition includes a filtering of the third force which estimates the force actually exerted to control the second amplitude; - 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; - the adjustment command is of the form:^^^^ℎ = ^^0 + ^^1cos (^^) + ^^2cos (2^^) + ^ + T^^cos (^^^^)where n is a strictly positive integer, T, ifor i integer between 1 and n denotes a constant term and θ denotes an angular position of the direction of the pilot mode relative to a reference axis of a reference frame linked to the housing, the reference axis being orthogonal to the sensitive axis; - a first adjustment command is provided during a first time interval 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 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. The invention also relates to a gyroscopic sensor comprising: - a housing; - 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 slave 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 to: a) exert on the vibrating element a first force configured so as not to disturb the measurement of the sensor from an adjustment command whose spectral signature is predetermined, b) to slave to a predetermined detection amplitude a second amplitude of vibrations of the vibrating element in the direction of the detection mode, and c) to exert a second force on the vibrating element, in 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 aestimation 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 directions x of the pilot mode and y of the detection mode and to exchange information with the first control module and with the second control 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 from a predetermined calibration angular velocity and from measurements of the vibrations of the vibrating element 15 transmitted by the measurement 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 velocitymeasured 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. According to another advantageous aspect of the invention, the first servo module and the second servo module comprise electrostatic excitation means. 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. 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: [Fig.1] Figure 1 is a schematic representation of a CVG according to the invention; [Fig.2] Figure 2 is a schematic representation of theoperation of the CVG of the prior art. [Fig. 3] Figure 3 is a schematic representation of the operation of the CVG of Figure 1; [Fig. 4] Figure 4 is a schematic representation of the trajectory of the vibrating element of Figure 1 and the directions of its pilot and detection modes in a spatial reference frame linked to the housing; [Fig. 5] Figure 5 is a representation in the form of a flowchart of a method according to the invention; [Fig. 6] Figure 6 is a partial representation of an electrostatic excitation device. [Fig. 7] Figure 7 is a representation in the form of a flowchart of a method of the prior art implemented on the CVG of Figure 2; and [Fig. 8] Figure 8 is a representation in the form of a detailed flowchart of the acquisition step 430 of the method of Figure 5. The Coriolis effect gyroscopic sensor 10, designated by the abbreviation CVG in the following, according to the invention is described with reference to Figure 1. The CVG 10 comprises ahousing 12 and a vibrating element 15 capable of vibrating relative to the housing 12. 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 made to vibrate by an electrical process. This arrangement makes it possible to minimize the size and / or the manufacturing cost of the CVG 10. Three axes X, Y, Z of the space reference frame XYZ of a reference frame (XYZ, t) linked to the housing 12 are shown in FIG. 4, the Z axis being of fixed direction in a space reference frame of an inertial reference frame. The CVG 10 is configured to measure an instantaneous angular velocity Ω(t) of the sensor relative to the Z axis, which therefore constitutes the sensitivity axis (or equivalently the sensitive axis) of the CVG 10. To this end, the vibrating element 15 comprises a test mass M, capable of vibrating in the XY plane along two axes:x and y directions, with a proper pulsation ω 0x , respectively ω 0y close to ω 0x . In the following, we consider that the direction x is the direction of the pilot mode and that the direction y is the direction of the detection mode. As visible in Figure 4, the angular position of the direction x of the pilot mode is identified by the angle θ defined with respect to the reference axis X of the space reference (XYZ) linked to the housing 12. The test mass M is able to vibrate in the direction x of the pilot mode x and the direction y of the detection mode, with a resonance pulsation ^ close to ω 0x The CVG 10 comprises a first servo module 20 capable of servo-controlling a characteristic amplitude of vibrations of the vibrating element 15 to a pilot amplitude x maxnon-zero predetermined, the vibrating element 15 vibrating in sinusoidal mode forced to the resonance pulsation ω 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. 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. As an example, which will be called a reference example in the following, the first servo module 20 comprises an electrostatic device 20A configured to exert a first force F x,ass in the x direction of the pilot mode on the vibrating element 15. The first force F x,assis then proportional to a first amplitude command. The electrostatic device 20A and the test mass M of the vibrating element 15 form, for example, a set of interdigital combs, as shown in Figure 6. The first amplitude command is a voltage V exc,x (t) imposed on the electrostatic device 20A by the servo module 20. In the case of figure 6, the force applied to the test mass M in the direction x of the pilot mode at an instant t is of the form F x,ass (t)=f geom V exc,x 2 (t) where: - f geom is a factor depending on the geometry of the combs, and - V exc,x is the voltage imposed by the generator. In general, the voltage V exc,x is of the form V exc,x (t) = V 0x + V 1x cos (ω t). Thus, the force actually applied to the test mass M is, after filtering the 2ω pulsation terms, of the form: [Math 1] The constant term of this force is not used in the following, since only the last term allows the proof mass M to oscillate. In other words, the non-sinusoidal terms are either naturally filtered or filterable by an appropriate filtering stage. In the end, it is therefore understood that the electrostatic device 20A can be configured by those skilled in the art to exert a first force F x,ass of pulsation substantially equal to the natural pulsation ω 0x 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 x max. 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. The processor or the programmable logic circuit is advantageously configured to manage the servo-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 ω. The CVG 10 comprises a second servo-control module 25 capable of servo-controlling a characteristic amplitude of vibrations of the vibrating element 15 according to the direction y of the detection mode to a detection amplitude y max, the vibrating element 15 vibrating in a forced sinusoidal regime along the direction y of the detection mode at the resonance pulsation ω, from measurement data of the position of the vibrating element along the direction y of the detection mode. 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). Thus, in the reference example, the second servo module 25 comprises an electrostatic device 25A configured to exert on the vibrating element 15 a second force F y,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 F y,phase,assis then proportional to a second amplitude command, on the principle described for the first servo module 20. 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. The processor or the 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.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 ω. The proximity card is in the reference example the same as that of the first control module 20. This arrangement is advantageous without being obligatory. The second control module 25 comprises an adjustment control unit 26, capable of receiving an adjustment command T. th and to be exercised from the adjustment command T th an additional force F y,phase,supp app whose direction is the y direction of the detection mode, in phase with the vibrations of the vibrating element 15 according to the x direction of the pilot mode. The spectral signature of the adjustment command T th , that is to say its decomposition into Fourier series, is known. The coefficients to T n(n strictly positive integer) of equation (a) below are therefore known. ^^^^ℎ = ^^0 + ^^1cos (^^) + ^^2cos (2^^) + ^ + T^^cos (^^^^) (a)For this purpose, the adjustment control unit 26 may comprise an electrostatic device 26A configured to actually exert an additional force F y,phase,supp app of the form F y,phase,supp app =T app x in response to the adjustment command T th , x being the position of the test mass M in the direction of the pilot mode. Typically, the electrostatic device 26A is a trimming comb polarized by a polarization voltage V T very stable and which is capable of exerting a force in the direction of the detection mode, directly proportional to the position x of the test mass M in the direction of the pilot mode and proportional to the square of the polarization voltage V T. 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 adjusting spontaneously to this position. 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: ^ ^ = V2 T.^^.^^ (b)This force is obtained by the physical design of the adjustment comb without it being necessary to estimate the position x of the proof mass. It is therefore directly proportional to x. In this case, we therefore understand that the polarization voltage V Tcan be controlled from the adjustment command, so that the theoretically controlled bias voltage verifies VT 2,th.^^ = ^^^^ℎ and the actually obtained bias voltage verifies VT,a 2pp.^^ = ^^^^^^^^ . It will be noted that the physical principle is entirely different from a force F AAwhich 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): ^^^^^^ = ^^0^^^^1^^.KAA.^^ (c) where ^^ denotes an estimator of the position x of the proof mass and not the actual position x of this proof mass. The adjustment comb is for example a quadrature adjustment comb, i.e. a comb involving a coupling between the pilot mode and the detection mode. 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. The control of the amplitude of the vibrations of the vibrating element 15 along the y direction of the detection mode is carried out by the second control module 25 in the presence of the additional force F y,phase,supp appactually applied. The second servo module 25 is also configured to actually apply a third force F y,quad app on the vibrating element 15, in the direction y of the detection mode and in phase quadrature with the additional force F y,phase,supp app , based on a spectral signature of the adjustment command T th and an estimate F y,phase,ass est of the second force F y,phase,ass app 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 F y,phase,supp appin two cases of movement of the sensor 10: - a first case, for which the instantaneous angular speed Ω(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 calibration angular speed Ω cal predetermined, and - a second case, for which the instantaneous angular speed Ω(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 speed Ω(t) is therefore unknown a priori, and to be determined. In this second case, the instantaneous angular speed is therefore not imposed, in particular on the calibration angular speed Ω calpredetermined, unlike the first case. 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 servo-controlling the vibrations of the vibrating element 15. 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. In particular, the measurement 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 d 2 x / dt 2 (t) (respectively d 2 y / dt 2(t)) along the x direction (respectively along the y direction). For this purpose, 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. Advantageously, the electrostatic detection means 30A and 30B each form, with the proof mass M, a set of interdigitated combs, on the geometric principle shown in FIG. 6. 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. The measurement module 30 is also configured to exchange information with a determination module 35 of the CVG 10.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. The determination module 35 is capable of determining a reference angular speed Ω. ref from the calibration angular velocity Ω cal 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. The determination module 35 is capable of determining in the second case of movement of the sensor 10 a measured instantaneous angular velocity Ω mes (t), which is an estimator of the angular speed Ω(t) sought, 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 from the reference angular speed Ω ref. The method 400 according to the invention will now be described with reference to figures 3, 5 and 8, in comparison with the method of the prior art represented in figures 2 and 7. The method 400 comprises an initialization step 410, a calibration step 420, an acquisition step 430 and a step 440 of determining the measured instantaneous angular velocity Ω mes (t). The initialization step 410 comprises: a) providing the first servo module 20 with the pilot amplitude x max non-zero 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) the supply to the second control module 25 of the detection amplitude y maxto which the characteristic amplitude of the vibrations of the vibrating element 15 in the direction y of the detection mode must be controlled, c) the supply to the adjustment control unit 26 of the adjustment command T th , whose spectral signature is known, and d) providing the determination module 35 with the calibration angular velocity Ω cal . The detection amplitude y max is for example zero. 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 pilot amplitude x maxnon-zero by means of the first servo module 20. The first servo module 20 receives for this purpose measurements of the vibrations of the vibrating element 15 in the direction x of the pilot mode from the measuring module 30. ii) simultaneously, the additional force F y,phase,supp app , the direction of which 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 command T th and the characteristic amplitude of the vibrations of the vibrating element 15 along the direction y of the detection mode is controlled by the detection amplitude y maxby means of the second servo module 25. The second servo module 25 receives for this purpose measurements of the vibrations of the vibrating element 15 in the direction y of the detection mode and in the direction x of the pilot mode from the measuring module 30. iii) the second servo module 25 determines the third force F y,quad app to be exerted on the vibrating element 15, in the direction y of the detection mode and in phase quadrature with the additional force F y,phase,supp app , based on an estimate F y,phase,ass est of the second force F y,phase,ass app actually exerted by the second servo device 25 to control 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,supp app . The third force F y,quad appis, 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 servo module 25 controls the exercise of the third force F y,quad app , 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 direction x of the pilot mode is controlled by the pilot amplitude x max non-zero by means of the first servo module 20, and the characteristic amplitude of the vibrations of the vibrating element 15 in the direction y is slaved to the detection amplitude y max in the presence of the additional force F y,phase,supp app actually applied. v) the determination module 35 determines the reference angular velocity Ω ref from the calibration angular velocity Ω calas well as measurements of the vibrations of the vibrating element 15 transmitted by the measuring module 30 to the first and second servo modules 20, 25 during iv. In the example, the additional force F y,phase,supp appis exerted in the y direction of the detection mode and in phase with the vibrations of the vibrating element 15 along the x direction. More generally, the additional force is exerted by means of a device making it possible to obtain a stable amplitude. The additional force is thus configured so as not to disturb the measurement carried out by the sensor. 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 / 100000. Generally, the additional force is thus configured so as not to disturb the measurement carried out by the sensor.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 Ω(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. 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 Ω. mes(t), which is an estimator of the instantaneous angular speed Ω(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 speed Ω ref determined in the calibration step 420. 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 with respect to the XYZ reference frame linked to the housing is described below. 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 K x and K y, as shown in Figure 1. 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, we can therefore write that K x = K y = K and that ω 0x = ω 0y = ω0. 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. In general, the trajectory of the mass M in forced sinusoidal mode is an ellipse in the xyZ frame of reference. 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 by a detection amplitude y max zero. Without making any assumption at this stage on the value of the detection amplitude y max, 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) = x max cos (ωt) 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) = y max sin (ωt). If the x direction of the pilot mode relative to the X axis of the XYZ frame linked to the box 12 is identified by the angle θ represented in figure 4, the X and Y coordinates of the mass m in the XYZ frame linked to the box 12 are linked to the x and y coordinates of the mass M in the xyZ frame by equation 2: [Math 2] in which R(θ) is the transition matrix from the xyZ frame to the XYZ frame: [Math 3] ^^(^^) = ^^^^^^^^ ‒ ^^^^^^^^[^^^^^^^^ ^^^^^^^^ ]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 Figure 2, as in the method 400 according to the invention, the transition matrix R(θ) is a function of time. In fact, in these processes, a rotation of the xyZ frame is controlled relative to the XYZ frame, therefore a temporal evolution of the angle θ, with the aim of eliminating the harmonic errors of the CVG 10. Furthermore, in gyroscope mode, the angle θ is free to evolve and the servocontrols are carried out in the xyZ frame. The first time derivatives dX / dt and dY / dt of the X and Y coordinates of the mass M therefore verify: [Math 4] The second time derivatives of 2 X / dt 2 and d 2 Y / dt 2the X and Y coordinates of the mass M verify: [Math 5] In a forced sinusoidal regime at pulsation ω, if we neglect the terms which are not proportional to a positive integer power of the pulsation ω in front of the other terms, equation 5 can be written in the simplified form of equation 6: [Math 6] In the frame of reference of box 12, the mass M is subjected to the forces F tot,x and F tot,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] The stiffness matrix K1 of the vibrating element 15, taking into account stiffness anisotropies, is of the form: [Math 8] 0 1 + ^^1 ^^2] [^^2 ‒ ^^1]Moreover, when the frame of reference of the box 12 is animated by a rotational movement of component Ω(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 box 12, is subjected to a Coriolis inertial force in this frame of reference of the box 12. Newton's second law applied to the mass M in the non-Galilean frame of reference of the box makes it possible to obtain equation 9: [ Math 9] 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. By neglecting the damping anisotropies, equation 9, after multiplication by R(-θ) and with the approximations of equation 5, is written as follows: [Math 10] enslaved to y max = 0, equation 10 takes the form: [ Math 11] 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 F tot,x in: [ Math 12] ^^^^^^^^,^^ = ^^^^,^^ℎ^^^^^^ + ^^^^,^^^^^^^^we obtain the system of equations 13: [Math 13] )^^ = ^^^^,^^ℎ^^^^^^ (1) The force F tot , x is the first force F x,ass exerted by the first servo module 20 for the servo-control of the amplitude of the vibrations according to the pilot mode to the pilot amplitude. Similarly, if we separate according to the direction y of the detection 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 F tot,y in: [Math 14] ^^^^^^^^,^^ = ^^^^,^^ℎ^^^^^^ + ^^^^,^^^^^^^^we obtain the system of equations 15: [Math 15] ‒ ^^ = (1) The term F y,phase , amplitude F y,phase,max, is managed by the second servo module 25 which receives the instruction to control the amplitude of the vibrations according to the detection mode at y max = 0 and the term F y,quad , amplitude F y,quad,max , is the third force imposed by the second servo module 25. 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 amplitude F y,quad,max non-zero, 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. The x and y directions of the pilot and detection modes then rotate at a pulsation dθ / dt different from the instantaneous angular velocity Ω(t) and we can at the same time: - reduce, or even eliminate, harmonic errors, by controlling a rotation of these directions by periodic modification of the direction of the third force F y,quad, and - deduce the instantaneous angular velocity Ω(t) from the measurement of dθ / dt according to equation 16: [ Math 16] II) PRIOR ART METHOD In the prior art methods, to obtain the third force F y,quad , the second control 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. This provides in particular the amplitudes and the pulsations of the different components of the voltage V exc,y (t), which must be in phase quadrature with the position x of the mass M. On the principle of equation 1, the electric voltage V exc,y (t) is typically of the form V exc,y (t) = V 0y + V 1y sin (ωt), so that the force F y,quad th theoretically applied to the mass M is proportional to the continuous component V 0yof the electrical voltage V exc,y (t) and a geometric factor g geom characteristic of the electrostatic excitation device 25B. In the case of the prior art methods, we therefore theoretically control: [Math 17] F y,q ^^ uℎ ad This control step is represented by step 510 of Figure 7, in which we observe that the force F y,quad th is commanded in order to cause a rotation of the pilot mode direction in the housing frame of reference at a command angular speed Ω com . The scale factor between the force F y,quad th commanded and the command angular velocity Ω com is constant and denoted C1. 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 V 0y, V 1y , as well as errors on the sinusoidal signal sin( ^^0^^ ) , the force F y,quad app actually applied to the test mass M differs more or less from the force F y,quad th controlled, both in amplitude and in phase. We can model the difference between the amplitude F y,quad,max th of the commanded force and the amplitude F y,quad,max app of the force actually applied by: [Math where e(t) is a very unstable error term due to the numerous electronic and mechanical parameters that cause it and C2 denotes a constant scale factor. Following the control step 510, the force F is therefore actually exerted during an acquisition step 520 y,quad app , which results in an effective rotation of the pilot mode direction in the housing frame of reference at an effective angular velocity Ω app different from the control angular speed Ω com. These two angular velocities are related by the following equation, in which C3 denotes a constant scale factor: In the prior art measuring method, the measured instantaneous angular velocity is deduced from equation 16 and the amplitude F y,quad,max th ordered for the third force F y,quad , which is provided during the initialization step to the second servo device 25, according to the formula: [Math 19] The effective instantaneous angular velocity Ω app , which would be deduced from equation 16 and the amplitude F y,quad,max app actually obtained for the third force F y,quad if it were perfectly known (that is to say if all the sources of errors were perfectly controlled and known), has the expression: [Math 20] The error made in the prior art method on the angular velocity therefore has the expression: [Math 21] This is therefore a scale factor type error. We understand that if the term 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 F y,quad th is zero. Moreover, 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 resolve this technical problem, by exerting a third force F y,quad appof better controlled amplitude 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 set 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 T th is implemented by the adjustment control unit 26 of the second servo module 25, so that the additional force F y,phase,supp app , of intensity T app |x|, in phase with the position x of the mass M and 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 following the direction y of the detection mode is carried out by the second control module 25 in the presence of the additional force F y,phase,supp appactually applied. The acquisition step 430 is shown in detail in Figure 8. The additional force F y,phase,supp app is actually applied in an application sub-step 4301. Due to the presence of the additional force, the system of equations 15 can therefore for the method of the invention be written in the form of the system of equations 22: [Math 22] with φ a constant value. For example, φ = 0 if adjustment combs of the quadrature comb type are used and, for example, φ = π / 2 if adjustment combs of the frequency comb type are used. The force F y,phase,ass app 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 expression: [Math 23] ^ ^^^,^^ℎ ^ ^^ ^^ ^^ ^^ ^^^,^^^^^^ = (^^2cos (2^^) ‒ ^^1sin (2^^) ‒ ^^^^^^^^cos (2^^ + ^^))^^We note that part of the force F y,phase,ass app intervenes to counter the additional force F y,phase,supp app applied through the injection of the adjustment command T th . During an estimation sub-step 4302 of the acquisition step 430, the servo-control device 25 estimates the force F y,phase,ass est to order to actually exert the force F y,phase,ass app on the vibrating element 15 for its control in the presence of the additional force F y,phase,supp app actually exerted by the adjustment unit 26. The force F y,phase,ass app is actually exercised during a first sub-step of exercise 4303, in the presence of the additional force F y,phase,supp app . We can model the difference between the force F y,phase,ass app actually applied to the sub-step of exercise 4303 and the estimator F y,phase,assest of the force to be commanded to exert this force, obtained in estimation sub-step 4302, by equation 24: [Math 24] The term ε(t) being much less than 1, we can still write, as was done in figure 8: [Math 25] F y,phas ^ e^^ ,^ a^^ ss,max = (1 ‒ ^^(^^))Fy,phas ^ e^^ ,^ a^ s^ s,max or again: [Math 26] ^ ^^^,^^ℎ ^ ^^ ^^ ^^ ^^ ^^ ^,^^^^^^ = (^^2cos (2^^) ‒ ^^1sin (2^^) ‒ ^^^^^^^^cos (2^^ + ^^))(1 ‒ ^^(^^))^^ Note that the term T app cos(2θ+φ) x is present in the force F y,phase,ass app and in the estimator F y,phase,ass est of the method 400 (unlike the methods of the prior art) due to the injection of the adjustment command T th . During an extraction sub-step 4304, the second servo device 25 extracts force F y,phase,assest thus estimated at least one estimator T i est of an amplitude T i app of the harmonic decomposition of T app , based on the spectral signature of the adjustment command T th . As a non-limiting example, we can choose T th of the form: [Math 27] ^^^^ℎ = ^^2cos (2^^ + φ)in which the angle θ designates the angular position of the direction x of the pilot mode relative to the reference axis X of the XYZ frame linked to the box 12. In this case, the average value of the term T app cos(2θ+φ) over a period characteristic of the variations of the angle θ is equal to T2 app / 2, so that it is possible to extract T2 app of the estimated force F y,phase,ass est by the servo device 25 and to evaluate T2 app, for example by filtering with an averaging filter. 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 i of the spectral signature of the adjustment command T th can be constant, or sinusoidal of the form T i = λ i cos(α i t + β i ) where α i , λ i and β i are predetermined constants. Then, during a control substep 4305, the processor of the servo device 25 controls the third force F y,quad th , of direction the y direction of the detection mode but in quadrature with the additional force F y,phase,supp th . As can be seen in Figure 8, the third force F y,quad th ordered includes a term proportional to each of the estimators T i est, the scale factor being constant and noted C4. During a second sub-step of exercise 4306, the control of the third force F y,quad th results in the exercise of the third force F y,quad app actually applied. The errors being the same in each of the sub-steps, the third force F y,quad app actually applied is in quadrature with the additional force F y,phase,supp app and it therefore ultimately actually includes a component proportional to each of the real harmonics T i app of T app used, the proportionality factor being constant and noted C5. Equation 16 can then be rewritten as follows, in which C6 denotes a constant scale factor: [Math 28] The third force F y,quad appactually applied therefore has the effect of imposing an additional angular speed of rotation on the wave frame, this additional angular speed being proportional to the amplitude T i app used. It is important to understand that the error made between the second estimated force F y,phase,ass est and the second force actually exerted F y,phase,ass app is the same as that between the third commanded force F y,quad th and the third force actually exerted F y,quad app , the conversion chain being the same in both cases. Consequently, if in the pre-calibration step 420, the predetermined angular velocity Ω cal was imposed on the box 12 with respect to the Z axis, with the same adjustment command T th , we also know, the conversion chain remaining the same, that: [Math 29] The additional angular velocity Ω appactually applied in the case of the method according to the invention is therefore exactly the reference angular speed Ω ref determined in the calibration step 420, and is not affected by the errors which occur in the prior art method, as can be seen in Figure 8. Thus, all that remains is to determine the instantaneous angular velocity Ω(t) sought using the reference angular velocity Ω ref determined at calibration step 420, according to equation 30: [ Math 30] 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. The only errors which affect the measurement are those linked to the implementation of the adjustment command T th, which must be as stable as possible between the calibration step 420 and the acquisition step 430. 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 an additional force F y,phase,supp app particularly stable. To best control these errors, it is advantageous to choose a 26A electrostatic excitation device whose geometry variations are as small as possible. For the same purpose, it is advantageous to choose a bias voltage source V T as stable as possible. Preferably, the bias voltage source V T includes filtering means configured to eliminate variable components of the voltage at its terminals. Advantageously, the instantaneous angular velocity Ω calof 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 Ω mes determined in determination step 440, in particular from equation 24. Advantageously, a first adjustment command T th is provided during a first time interval t1 and a second adjustment command which is the opposite of the first adjustment command T this 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 t1 and in a direction opposite to the first direction during the second time interval t2. 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. Equivalently, during the control substep 4305, a first sign can be applied during a first time interval t1, so that the third commanded force F y,quad th 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 commanded force F y,quad thhas a direction opposite to the first direction during the second time interval t2. In summary, the method 100 according to the invention has the following specific features. 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 F y,phase,supp app very stable, unlike prior art methods. The additional force F y,phase,supp app can be obtained in particular by means of adjustment combs, the stability of the additional force therefore depending on the stability of the tensions used and the air gaps of the adjustment combs. The stability of the additional force F y,phase,supp appis 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. Secondly, the angular velocity suppressed at the output to compensate for the precession control, i.e. the third force F y,quad app , is directly proportional to the magnitude of the additional stable force F y,phase,supp app injected at the input, and is not the angular velocity associated with an electronically injected precession command, which is intrinsically unstable. Third, by playing on the signs of the adjustment command, it is possible to choose the direction of the third force F y,quad appand 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. If the first duration and the second duration are suitably chosen, the scale factor errors can be eliminated precisely. This is not the case in the methods of the prior art due to the instability of the scale factor. It will be noted that the stable force injected at the input does not reduce the performance of the gyroscopic measuring device. As indicated previously, the additional force is exerted by means of a device making it possible to obtain a stable amplitude for this force, for example 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 / 100000.As an illustrative example, to be able to perform an average over all the angular positions traveled by the direction of the pilot mode of the vibrating element due to the rotation command injected for an instantaneous angular velocity measurement of the housing, the angular command velocity is of the order of a few degrees per second, for example close to 5° / s. If the precision on the amplitude of the additional force is of the order of 10 ppm, the command of the additional force induces a drift locally of the order of 10 ppm* 5° / s*3600 = 0.18° / h. Such an error can be considered acceptable for a gyroscopic sensor. For example, the Earth's rotation is approximately 15° / h in absolute terms, i.e. before projection as a function of latitude, so that an error of the order of 0.18° / h makes it possible to determine the carrier's heading autonomously.In general, the tolerance on the amplitude of the additional force can be adjusted, thanks to the particular embodiment of this force described above, depending on the precision required for the measurements and / or the limits of the dynamics of the carrier that the gyroscopic sensor equips. In summary, the additional force is configured so as not to disturb the measurement carried out by the sensor in the sense that it has an effect on the measurement which ultimately allows the error on the measurement to be reduced, thanks to the great stability of its amplitude, permitted by the method according to the invention.

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 (x) is provided max ), a detection amplitude (y max ), an adjustment command (T th ) whose spectral signature is predetermined, and a calibration angular velocity (Ω cal ); - calibration (420), comprising: i) control to the pilot amplitude (x max ) 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 exercise of a first force (F y,phase,suppapp ) on the vibrating element (15) configured so as not to disturb the measurement of the sensor (10) from the adjustment command (T th ), and the control of the detection amplitude (y max ) of a second amplitude of vibrations of the vibrating element (15) in the direction (y) of the detection mode, iii) simultaneously, the exercise of a second force (F y,quad app ) on the vibrating element (15), along the direction (y) of the detection mode and in phase quadrature with the first force, the second force (F y,quad app ) being determined on the basis of a third force (F y,phase,ass est ) which estimates the force actually exerted to control the second amplitude and the spectral signature of the adjustment command (T th) and being configured to cause a rotation of the direction (x) of the pilot mode relative to the housing (12), an instantaneous angular speed (Ω(t)) of the housing (12) relative to a sensitive axis (Z) being imposed and equal to the calibration angular speed (Ω cal ) during i), ii) and iii); iv) the determination of a reference angular velocity (Ω ref ) from the calibration angular velocity (Ω cal ) 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 (Ω(t)); - determination (440) of a measured instantaneous angular velocity (Ω mes (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 speed (Ω ref).

2. Method (400) of gyroscopic measurement according to claim 1, in which for the calibration (420), the first force (F y,phase,supp app ) 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 (Ω cal ) is zero.

4. Method according to any one of the preceding claims, in which the detection amplitude (y max ) 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) comprise a filtering of the third force (F y,phase,ass est) 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 (F y,phase,supp app ) 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 (T th 7. Method according to any one of the preceding claims, in which the adjustment command (T th ) is of the form:^^^^ℎ = ^^0 + ^^1cos (^^) + ^^2cos (2^^) + ^ + T^^cos (^^^^)where n is a strictly positive integer, T i for i integer between 1 and n denotes a constant term and θ denotes an angular position of the direction (x) of the pilot mode relative 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. Method according to any one of the preceding claims, in which a first adjustment command (T th ) 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), 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. 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 (x max) and slave to a pilot amplitude (x max ) predetermines 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) exert on the vibrating element (15) a first force (F y,phase,supp app ) configured so as not to disturb the measurement of the sensor (10) from an adjustment command (T th ) whose spectral signature is predetermined,b) subject to a detection amplitude (y max ) predetermines a second amplitude of vibrations of the vibrating element (15) in the direction (y) of the detection mode, and c) exerting a second force (F y,quad app ) on the vibrating element (15), along the direction (y) of the detection mode and in phase quadrature with the first force, the second force (F y,quad app) being configured to cause a rotation of the direction (x) of the pilot mode relative to the housing (12), the second force (F y,quad app ) being determined on the basis of a third force (F y,phase,ass est ) which is an estimate of the force actually exerted to control the second amplitude and of the spectral signature of the adjustment command (T th ); - 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 (Ω ref) from a calibration angular velocity (Ω cal ) predetermined 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 (Ω(t)) of the housing (12) relative to a sensitive axis (Z) is imposed and equal to the calibration angular speed (Ω cal ), and ii) a measured instantaneous angular velocity (Ω mes (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 (Ω(t)) is free and from the reference angular velocity (Ω ref).

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

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