Measurement method and gyroscopic sensor

Abstract

The present invention relates to a method (400) for 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), which method comprises providing a first closed-loop control module (20) with a first force (Fx) to be applied in the direction of the pilot mode (x) on the vibrating element (15) and a pilot amplitude (xmax) for closed-loop control of the vibrations in the direction of the pilot mode (x); simultaneously implementing the first force (Fx) and the closed-loop control of the vibrating element (15) in the direction (x) of the pilot mode; providing a second closed-loop control module (25) with a second force (Fy) to be applied in phase quadrature with the first force in the direction of the detection mode (y) and a non-zero detection amplitude (ymax) for closed-loop control of the vibrations in the direction (y) of the detection mode; simultaneously implementing the second force (Fy) and the closed-loop control in the direction (y) of the detection mode; and determining an instantaneous angular velocity (Ω(t)) of the housing in an inertial reference system.

Description

[0001] TITLE: Measurement method and gyroscopic sensor

[0002] The present invention relates to a gyroscopic measurement method.

[0003] 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.

[0004] A Coriolis Vibratory Gyroscope (CVG) sensor can measure the component along an axis, called the sensitivity axis, of an instantaneous rotation speed vector of a frame of reference linked to a sensor housing relative to an inertial frame of reference.

[0005] The CVG therefore includes a vibrating element of the sensor capable of vibrating relative to the housing. The measurement is carried out using the effects of the Coriolis inertial force exerted on the vibrating element.

[0006] The vibrating element of a CVG is capable of vibrating along two coplanar vibration directions, called the pilot mode direction and the detection mode direction, with the work of the Coriolis force allowing a transfer of mechanical energy between the two directions.

[0007] The CVG sensitivity axis is orthogonal to the plane of the pilot mode and detection mode directions.

[0008] For the measurements, the vibrating element is excited along the direction of the pilot mode at its resonant frequency by the excitation system. The amplitude of the vibrations along the pilot mode is kept constant by means of a voltage control system 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.

[0009] 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 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 rotational speed vector.

[0010] 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 frame of reference 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 related to CVG defects. These defects include stiffness or damping anisotropies of the vibrating element, defects in the excitation control electronics or the vibrating element position detection electronics, defects in the reference electrical voltage for 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 position of the directions of the pilot mode and the detection 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 that 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 that is based on the difference between the measurement signal and the control signal.

[0017] However, due to errors in the chain of conversion of 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 in the angle measurement may be zero over a period characteristic of the variations in the control signal. However, this is very unlikely, as the sources of error are numerous and of different natures. These include detection errors in the detection combs, excitation errors in the excitation combs, as well as instabilities in 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.

[0019] Ultimately, in most situations, the average value of the error committed is not zero over a period of the alternating rotation of the sensor position. Moreover, during the round trip of the wave, the angular errors of the sensor are all the greater as the defects mentioned above are significant.

[0020] Such a device reduces the impact of defects on the measurement without allowing the measurement error linked to these defects to be assessed.

[0021] Furthermore, the control signal used in FR 2937414 must allow a 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 a zero-mean control signal to be obtained at the same time as returning to the same angular position.

[0022] An aim of the invention is then to propose a gyroscopic measurement method making it possible to estimate certain measurement errors, in particular harmonic anisotropy errors, in order to take them into account in the measurement result, and thus to obtain a measurement result of known, or even improved, precision, independently of the nature of the movement of the sensor in an inertial frame of reference.

[0023] To this end, the invention relates to a method of gyroscopic measurement using 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:

[0024] - supplying to a first servo module of the sensor: a) a first amplitude of a first force to be exerted in the direction of the pilot mode on the vibrating element, and b) a predetermined non-zero pilot amplitude to which a characteristic amplitude of the vibrations in forced sinusoidal mode of the vibrating element in the direction of the pilot mode must be servo-controlled; and

[0025] - the simultaneous implementation of the first force on the vibrating element and the control of the characteristic amplitude of the vibrations in forced sinusoidal mode of the vibrating element in the direction of the pilot mode by means of the first control module receiving measurements of the vibrations of the vibrating element in the direction of the pilot mode from a module for measuring the vibrations of the vibrating element; the method being characterized in that it further comprises:

[0026] - supplying to a second servo module: c) a second amplitude of a second force to be exerted in phase quadrature with the first force along the direction of the detection mode, and d) a predetermined non-zero detection amplitude to which a characteristic amplitude of the vibrations of the vibrating element along the direction of the detection mode must be controlled; and

[0027] - the simultaneous implementation of the second force on the vibrating element and the control of the characteristic amplitude of the vibrations of the vibrating element along the direction of the detection mode by means of the second control module receiving measurements of a position of the vibrating element along the direction of the detection mode from the measurement module; and

[0028] - determining, by means of a sensor determination module, an instantaneous angular velocity of the housing in an inertial frame of reference from the first and second amplitudes of the first and second forces, the non-zero pilot and detection amplitudes, as well as measurements of the vibrations of the vibrating element transmitted by the measurement module to the first and second servo modules.

[0029] The vibrating element is excited both in the direction of the pilot mode and in the direction of the detection mode, not only under the effect of the two forces of predetermined amplitudes but also of the servocontrol.

[0030] The vibrating element oscillates with a non-zero amplitude along the direction of the pilot mode as in the prior art methods. Unusually, the vibrating element also oscillates with a non-zero amplitude along the direction of the detection mode.

[0031] The control of the vibration amplitude according to the detection mode to a non-zero value is carried out by implementing a force in the direction of the detection mode, the evaluation of which makes it possible, in combination with the evaluation of the force actually implemented to carry out the control of the vibration amplitude according to the pilot mode, to estimate the damping anisotropy errors of the vibrating element. These estimated errors can then be taken into account quantitatively in the step of determining the angular speed of the housing. Thus, the accuracy of the gyroscopic measurement is improved compared to the methods of the prior art, in which these errors are minimized without however being evaluated. According to other advantageous aspects of the invention, the measurement method comprises one or more of the following characteristics, taken individually or in all technically possible combinations:

[0032] - the ratio of the pilot amplitude and the detection amplitude is less than 100;

[0033] - the vibrations of the vibrating element are characterized by a pulsation different from the natural pulsation of the vibrating element, the relative difference between the pulsation and the natural pulsation being less than 10%, preferably of the order of 1% or less;

[0034] - the method further comprises a step of determining a characteristic pulsation of the vibrations of the vibrating element by means of the determination module, from the measurements of the positions of the vibrating element transmitted by the measurement module to the first and second servo modules.

[0035] - the implementation of the first force and the second force on the vibrating element comprises a step of determining a characteristic matrix of an anisotropy of the vibrating element from an amplitude of a third force and an amplitude of a fourth force actually exerted by respectively the first servo module and the second servo module to respectively servo the characteristic amplitude of the vibrations of the vibrating element in the direction of the pilot mode and the characteristic amplitude of the vibrations of the vibrating element in the direction of the detection mode.

[0036] The invention also relates to a gyroscopic sensor comprising:

[0037] - a case;

[0038] - 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;

[0039] - a measurement module capable of generating measurements of the vibrations of the vibrating element according to the directions of the pilot mode and the detection mode;

[0040] - a first servo-control module capable of: i) exerting a first force, the amplitude of which is equal to a first predetermined amplitude, on the vibrating element in the direction of the pilot mode, ii) simultaneously servo-controlling a characteristic amplitude of vibrations of the vibrating element in forced sinusoidal mode in the direction of the pilot mode to a predetermined non-zero pilot amplitude, iii) receiving measurements of the vibrations of the vibrating element in the direction of the pilot mode from the measurement module to carry out this servo-control; the sensor being characterized in that it comprises:

[0041] - a second servo-control module capable of: iv) exerting a second force, the amplitude of which is equal to a second predetermined amplitude, on the vibrating element in the direction of the detection mode, the second force being in phase quadrature with the first force, v) simultaneously servo-controlling a characteristic amplitude of the vibrations of the vibrating element in the direction of the detection mode to a non-zero detection amplitude, vi) receiving measurements of the vibrations of the vibrating element in the direction of the detection mode from the measurement module to carry out this servo-control; and

[0042] - a determination module capable of determining an instantaneous angular velocity of the housing in an inertial frame of reference from the amplitudes of the first force and the second force, the non-zero pilot amplitude and the non-zero detection amplitude, as well as measurements of the vibrations of the vibrating element transmitted by the measurement module to the first and second servo modules.

[0043] The invention also relates to a computer program comprising instructions which cause the sensor as described above to carry out the step of determining the instantaneous angular velocity of the housing of the method according to any one of the preceding embodiments.

[0044] 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:

[0045] [Fig. 1] Figure 1 is a schematic representation of a CVG according to the invention;

[0046] [Fig. 2] Figure 2 Part A is a schematic representation of the operation of the prior art CVG; Figure 2 Part B is a schematic representation of the operation of the CVG of Figure 1;

[0047] [Fig. 3] Figure 3 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 frame related to the housing; and

[0048] [Fig. 4] Figure 4 is a flowchart representation of a method according to the invention.

[0049] The Coriolis effect gyroscopic sensor 10, hereinafter referred to as CVG, according to the invention is described with reference to FIG. 1.

[0050] The CVG 10 comprises a housing 12 and a vibrating element 15 capable of vibrating relative to the housing 12.

[0051] The CVG 10 is for example produced in the form of a microelectromechanical system (MEMS). The vibrating element 15 and the housing 12 are then cut from a block of silicon or quartz by micromachining and the vibrating element 15 is set into vibration by an electrical process. This arrangement makes it possible to minimize the size and / or the manufacturing cost of the CVG 10.

[0052] Three axes X, Y, Z of the XYZ space frame of a reference frame linked to the housing 12 are represented in FIG. 1, the Z axis being of fixed direction in a space frame of an inertial reference frame.

[0053] 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 of the CVG 10.

[0054] To this end, the vibrating element 15 is capable of vibrating in the XY plane in two directions x and y, with a specific pulsation œ, respectively w.

[0055] 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.

[0056] The CVG 10 comprises a first servo module 20 capable of servo-controlling a characteristic vibration amplitude of the vibrating element 15 to a pilot amplitude x ma x non-zero predetermined, the vibrating element 15 vibrating in sinusoidal mode forced to a 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.

[0057] The first servo module 20 comprises conventional 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.

[0058] 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 F on the vibrating element 15. x ,am P direction the x direction of the pilot mode. The first force F x , am p is then proportional to a first amplitude command.

[0059] 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.

[0060] The first servo module 20 is capable of receiving a first predetermined amplitude Fx.max of a second force F xand to exert this second force on the vibrating element 15 in the x direction of the pilot mode.

[0061] In the example described above, the electrostatic device 20A is thus configured to exert the second force F x direction the x direction of the pilot mode and amplitude F x , max . The second force F x is then proportional to a stiffness command, which is sent by the processor or programmable logic circuit and injected into the 20A electrostatic device by means of the proximity card.

[0062] The processor or 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.

[0063] As we will see later, the second force F x , of amplitude F x , max predetermined, is different from the first force F x ,amp , which is intended to combat the damping of the vibrations of the vibrating element 15 in the x direction of the pilot mode to keep the amplitude of the vibrations constant in the x direction of the pilot mode.

[0064] The first servo module 20 is therefore configured to exert on the vibrating element 15 a total force F to t, x following the x direction of the pilot mode which is the resultant of the first force F x , am p and the second force F x , the control of the amplitude of the vibrations of the vibrating element 15 according to the direction x of the pilot mode being carried out in the presence of the second force F x .

[0065] The CVG 10 comprises a second servo module 25 capable of servo-controlling a characteristic amplitude of the vibrations of the vibrating element 15 along the direction y of the detection mode to a detection amplitude y max non-zero, the vibrating element 15 vibrating in forced sinusoidal mode along the direction y of the detection mode at a pulsation w, from measurement data of the position of the vibrating element along the direction y of the detection mode.

[0066] To this end, the second servo module 25 comprises servo means similar to those of the first servo module 20 (not shown in detail).

[0067] Thus, in the reference example, the second servo module 25 comprises an electrostatic device 25A configured to exert a third force Fy on the vibrating element 15, am p direction the y direction of the detection mode. The third force Fy, a mp is then proportional to a second amplitude command.

[0068] The second servo module 25 comprises, in the reference example, a processor or a programmable logic circuit (“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 a programmable logic circuit (such as a “Field Programmable Gate Array”, FPGA) is, in the reference example, the same as that of the first servo module 20. This arrangement is advantageous without being obligatory.

[0069] The processor or 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.

[0070] 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.

[0071] The third force F y , a mp is intended to keep the amplitude of the vibrations along the y direction of the detection mode equal to the detection amplitude y ma x not zero. It is therefore different from the force exerted in the prior art according to the detection mode, for example by means of a quadrature command sent to the electrostatic device 25 A in order to cancel the amplitude of the vibrations according to the detection mode.

[0072] The second servo module 25 is capable of receiving a second amplitude F y ,m ax of a fourth force F y to be exerted on the vibrating element 15 in the y direction of the detection mode.

[0073] In the reference example, the electrostatic device 25A is thus configured to exert a fourth force F y direction the y direction of the detection mode and amplitude the second amplitude F y , ma x. The fourth force F y is then proportional to a precession command, which is sent by the processor or the FPGA and injected into the electrostatic device 25A by means of the proximity card.

[0074] As we will see later, the fourth force F y , of amplitude F y , ma x predetermined, is different from the third force F y , a m P , which is intended to combat the damping of the vibrations of the vibrating element 15 in the direction y of the detection mode to keep the amplitude of the vibrations constant in the direction y of the detection mode.

[0075] The second servo module 25 is therefore configured to exert on the vibrating element 15 a total force F to t, y following the y direction of the pilot mode which is the resultant of the third force F y , am p and the fourth force F y , the control of the amplitude of the vibrations along the y direction of the detection mode being thus achieved in the presence of the third force.

[0076] The CVG 10 comprises a measurement module 30 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, with the second servo module 25.

[0077] 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 d 2 x / dt2 (t) (respectively d 2 y / dt 2 (t)) along the x direction (respectively along the y direction).

[0078] 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.

[0079] In the reference example, the proximity card is advantageously configured to amplify the signals detected by the measurement module 30 and to transmit the amplified signals to the processor or the programmable logic circuit.

[0080] The measurement module 30 is also configured to exchange information with a determination module 35 of the CVG 10.

[0081] 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.

[0082] The determination module 35 is capable of determining an instantaneous angular velocity Q(t) of the housing 12 at a date t in the inertial frame of reference from:

[0083] - measurements of the vibrations of the vibrating element 15 generated by the measuring module 30,

[0084] - of the first amplitude F x , max ,

[0085] - of the second amplitude F y , max ,

[0086] - of the pilot amplitude x max non-zero,

[0087] - and the detection amplitude y max non-zero.

[0088] Advantageously, the determination module 35 is capable of determining a pulsation w characteristic of the vibrations of the vibrating element 15 according to the pilot mode and / or respectively according to the detection mode.

[0089] The CVG 10 operates as a gyroscopic sensor insofar as the instantaneous angular velocity Q(t) of the housing 12 is determined by the determination module 35.

[0090] The gyroscopic measurement method 400 implemented by means of the CVG 10 will now be described with reference to figure 2 part B and to figure 4.

[0091] To simplify the writing of the equations allowing this process to be understood, 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.

[0092] Furthermore, we consider 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 w O x = wo y = wo. This simplification should in no case be considered as limiting for the operation of the sensor according to the invention, the following equations can be rewritten without difficulty in the most general case.

[0093] Method 400 comprises:

[0094] - a forcing step 410 comprising the simultaneous exercise of the second force F x by means of the first servo module 20 and the fourth force F y by means of the second servo module 25, the amplitudes of the vibrations of the vibrating element being simultaneously controlled respectively to the pilot amplitude x manon-zero x and detection amplitude y ma x not zero,

[0095] - followed by a step 420 of determining the instantaneous angular speed Q(t) of the box 12 in the inertial frame of reference.

[0096] In the forcing step 410, the mass M is excited so as to vibrate in a forced sinusoidal regime at the pulsation w along the direction x with the amplitude x max non-zero, while the second force F x is exerted on the mass M in the x direction of the pilot mode.

[0097] For this, the first servo module 20 receives from the module 30 measurements of the vibrations of the mass M in the direction x of the pilot mode and exerts the first force F x , amp .

[0098] The first servo module 20 thus simultaneously exerts the second force F x and the first force F x , ampwhich is configured to keep the amplitude of the vibrations of the vibrating element 15 constant in the x direction.

[0099] The first and second forces are in phase quadrature with each other and co-pulsation.

[0100] During the forcing step 410, the vibrating element 15 is therefore subjected in the direction x by the first servo module 20 to the force F to t,x, which is the resultant of the second force F x and the first force F x , amp .

[0101] Simultaneously, the mass M is excited so as to vibrate in a forced sinusoidal regime at the pulsation co along the direction y of the detection mode, with the amplitude y max non-zero and in phase quadrature with the oscillations along the x direction of the pilot mode, while the fourth force F y is exerted on the vibrating element 15.

[0102] To do this, the second servo module 25 receives from the module 30 measurements of the vibrations of the mass M along the direction y of the detection mode, and it exerts the third force F y , amp on the mass M. The third force F y , amp has the direction y of the detection mode and is in phase quadrature with the first force F x , a mp- The second servo module 25 thus simultaneously exerts the fourth force F y and the third force F y , amp configured to keep the amplitude of the vibrations of the vibrating element 15 constant in the direction y.

[0103] The third and fourth forces Fy, amp and F y are in quadrature with each other, and the fourth force is in phase quadrature with the second force F x .

[0104] During the forcing step 410, the vibrating element 15 is therefore subjected in the direction y by the second servo module 25 to the force F to t. y , which is the resultant of the fourth force F y and the third force F y , amp .

[0105] During the forcing step 410, the mass M is therefore excited by means of the first servo module 20 and the second servo module 25 so as to vibrate in a forced sinusoidal regime at the pulsation w along the direction x with the amplitude x max non-zero as in the methods of the prior art, as well as, along the direction y with the amplitude y ma x non-zero, unlike the sensors of the prior art in which the vibrating element 15 is not subjected to any forced excitation according to the detection mode y, at the same pulsation w as according to the pilot mode but in phase quadrature.

[0106] In method 400, the mass M is therefore simultaneously excited simultaneously in the direction x by a second force of the form F x = F x , ma x Cos (wt) and along the y direction by a fourth quadrature force, of the form F y = F y , max sin (eut) in addition to the first force F x , amp and the third force F y , amp intended to control the amplitudes of the vibrations according to the pilot and detection modes.

[0107] It will be shown later that during the forcing step 410, due to the presence of the second force F x and the fourth force F y , the vibrating element 15 vibrates at a pulsation w different from but close to the natural pulsation CÜO.

[0108] If, in a step prior to the forcing step 410, the vibrating element is excited at its own pulsation cuo in the absence of a second force, the amplitude of the vibrations according to the detection mode being controlled to a zero value, a shift in the pulsation of the vibrations from the own pulsation CÜO to the pulsation eu will occur spontaneously during a transient phase at the start of the forcing step 410.

[0109] In the determination step 420, the determination module 35 determines the instantaneous angular velocity Q(t) in the inertial frame of reference.

[0110] The determination module 35 receives for this:

[0111] - measurement results of the vibrations of the vibrating element 15 from the measuring module 30,

[0112] - the amplitude F x , ma x of the first force and the amplitude F y , max of the second force,

[0113] - as well as the amplitudes xmax and there max The processor of the determination module 35 then implements a model for determining the instantaneous angular velocity Q(t) to determine this angular velocity from the received data.

[0114] The model for determining the instantaneous angular velocity Q(t) can include explicit equations based on the fundamental principle of dynamics.

[0115] In particular, in the method 400 according to the invention, due to the particular design of the forcing step 410, 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 ma x cos (wt) 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 (wt).

[0116] The trajectory of the mass M is therefore an ellipse in the xyZ frame, unlike the methods of the prior art for which the trajectory of the mass M is a straight line segment in direction x.

[0117] 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 0 represented in figure 3, 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 the equation 1:

[0118] [Math 1] with [Math 2]

[0119] The first time derivatives dX / dt and dY / dt of the X and Y coordinates of the mass M therefore verify:

[0120] [Math 3]

[0121] The second time derivatives of 2 X / dt 2 and d 2 Y / dt 2 the X and Y coordinates of the mass M verify:

[0122] [Math 4] 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 4 can be written in the simplified form of equation 5:

[0123] [Math 5]

[0124] X x — 29ÿ

[0125] = / ?(0)

[0126] Ÿ. 26x + ÿ

[0127] In the frame of reference of the box 12, the mass M is subjected during the forcing step 410 to the first force F x , a m P , to the second force F x , to the third force F y , amp , at the fourth force F y , to the restoring forces of the springs, as well as to damping which is modeled by a fluid friction force along each of the x and y directions associated with a quality factor Q.

[0128] The damping matrix A of the vibrating element 15, taking into account damping anisotropies, is of the form described in equation 6:

[0129] [Math 6] 01 [al a2 1 1J + La2 -garlic

[0130] The stiffness matrix K1 of the vibrating element 15, taking into account stiffness anisotropies, is of the form:

[0131] [Math 7]

[0132] 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 housing 12.

[0133] Newton's second law applied to the mass M in the non-Galilean frame of reference of the box allows us to obtain equation 8:

[0134] [Math 8] or, after multiplication by R(-9) and with the approximations of equation 5:

[0135] [Math 9]

[0136] The left-hand side of the equation shows a damping anisotropy term of the form: [Math 10] whose component has x following the direction of the pilot mode x is worth:

[0137] [Math 11]

[0138] = a l x x + a2, x ÿ and whose component a y depending on the direction of the detection mode y is worth:

[0139] [Math a y =

[0140] = a y X + a2,yy

[0141] = «2, xx - a l x ÿ

[0142] The first term ai, x dx / dt of the a component x of the damping anisotropy term, i.e. the term proportional to dx / dt, is compensated by means of the first force F x , amp. It is therefore compensated in the reference example by means of the first amplitude command of the first servo module 20.

[0143] The second term O2, x dy / dt of the component a x of the damping anisotropy term, which is proportional to dy / dt, is compensated by means of the second force F x . It is therefore compensated in the reference example by means of the stiffness control of the first servo module 20.

[0144] The first force F x ,am P therefore has the expression

[0145] [Math 13]

[0146] The second term 02, y dy / dt of the component a y of the damping anisotropy term, that is the term proportional to dy / dt, is observable precisely because the vibration amplitude along the direction of the detection mode is fixed at a non-zero value y max.

[0147] It is compensated by means of the third force F y.a m P , therefore in the example described above by means of the second amplitude control of the second servo module 25.

[0148] The third force F y , amp therefore has the expression

[0149] [Math 14]

[0150] We see that the third force F y , amp is proportional to dy / dt and therefore only exists because the motion of the vibrating element in the xyZ frame is elliptical and not rectilinear. The third force F y , amp is very different from that used in the prior art for the control of the amplitude of the vibrations in the direction y has a zero value.

[0151] We also note that the amplitudes F x , amp ,max and F y , amp ,max of the first and third forces verify

[0152] [Math 15]

[0153] The control of the vibration amplitudes to a non-zero value not only in the x direction but also in the y direction therefore makes it possible to determine the anisotropy matrix.

[0154] The coefficients a1 and a2 can in particular be deduced from equation 15 as soon as we have measurements for several different angles 0.

[0155] Such a determination is not possible in a prior art gyroscope, for which only equation 13 is available, the terms of equation 14 being null. Indeed, the term Mœ0 / Q is strongly dependent on the temperature of the vibrating element 15 so that it is not possible to deduce a1 and a2 from equation 13 alone.

[0156] In the reference example, the processor common to the first servo module 20 and to the second servo module 25 therefore determines the first force F x , amp and the third force F y ,amp which are actually exerted by these servo modules 20 and 25 to obtain the desired amplitude servo control along the x and y directions. It deduces the expression of the coefficients a1 and a2 of the anisotropy matrix.

[0157] In the end, if we neglect the harmonic errors linked to the stiffness anisotropies (corresponding to the terms r1 and r2) and with the approximations made for equation 5, Newton's second law applied to the mass in the non-Galilean frame of reference linked to the box 12 allows, after simplification by means of equations 13 and 14 and grouping of the terms in phase with the vibrations along the x direction and of the terms in phase quadrature with these vibrations, to write the two equations 16 and 17 which follow:

[0158] [Math 16] where F x , max is the first amplitude, that is, the amplitude of the second force F xto be supplied to the first servo module 20, and [Math 17] cil sin(20))ivx ma ^ where Fy, max is the second amplitude, i.e. the amplitude of the fourth force F y to be supplied to the second servo module 25.

[0159] In the methods of the prior art, the excitation pulsation co is approximately equal to the natural pulsation oo0 and y ma x = 0.

[0160] On the contrary, in the method 400 according to the invention, the amplitude y ma x is fixed and equal to a predetermined non-zero value, as is the amplitude x ma x.

[0161] Furthermore, we have seen that the coefficients of the anisotropy matrix are precisely determined from the third force Fy, am p.

[0162] These coefficients make it possible to correct in real time the anisotropy defects appearing in equations 16 and 17, so that in the end, the second and fourth forces have the expression after correction in real time by the control modules 20,25 of the anisotropy defects made accessible:

[0163] [Math 18]

[0164] [Math 19]

[0165] The anisotropy errors are therefore known and managed in the method 400, unlike the methods of the prior art.

[0166] In the method 400 according to the invention, it is understood with equations 18 and 19 that the angle 9 which characterizes the direction x in the XY frame is not constant due to the application of the second force and the fourth force and that, with the approximations which have been made, this angle verifies equation 20:

[0167] [Math 20]

[0168] The x direction of the pilot mode and the y direction of the detection mode will therefore vary over time in the XYZ frame of reference of the housing 12 due to the second and fourth forces applied simultaneously in these two directions.

[0169] In the determination step 420, the determination module 35 can deduce the instantaneous angular velocity Q(t) of the sensor relative to the Z axis from the data that it receives from the measurement module 30, which makes it possible to determine d0 / dt, from the first amplitude F x , ma x, of the second amplitude F y , ma x, as well as amplitudes x ma x and y max and the following equation 21:

[0170] [Math 21]

[0171] It will be noted that the measurement results provided by the measurement module 30 also allow the determination module 35 to estimate the pulsation co of the vibrations of the vibrating element 15.

[0172] As previously stated, the co pulsation is close to the proper co pulsation o of the vibrating element, therefore is an estimator of this proper pulsation, which can be injected into equation 21 to determine the instantaneous angular velocity Q(t).

[0173] Equations 18 and 19 in fact allow us to form the following equation 22 on the co pulsation:

[0174] [Math 22]

[0175] It should also be noted that it is possible to adjust one and / or the other of the predetermined amplitudes F x , ma x and F y , ma x to increase or decrease the pulsation slip relative to the natural pulsation co o .

[0176] Advantageously, the relative difference between the co pulsation and the COQ proper pulsation is less than 10%, preferably of the order of 1% or less.

[0177] Typically, the natural pulsation can be of the order of 10 Hz. The relative difference between the co pulsation and the natural pulsation coo can then be less than 1 Hz, and in particular be typically of the order of a tenth of Hz.

[0178] Since the implementation of non-zero amplitude vibrations depending on the detection mode is likely to introduce errors in the measurement of the angular velocity Q(t), it is advantageous to make a compromise between the management of anisotropies permitted by the detection amplitude y ma x not zero and these new errors.

[0179] Advantageously, the ratio of the pilot amplitude x max and the detection amplitude y ma x is less than 10, or even less than 100.

[0180] Advantageously, the detection amplitude y ma x is of the order of 1 / 100 ème , or even of the order of 1 / 1000 ème of the pilot amplitude Xmax-

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: - supplying to a first servo module (20) of the sensor: a) a first amplitude (F x , ma x) of a first force (F x ) to be exerted in the direction of the pilot mode (x) on the vibrating element (15), and b) of a pilot amplitude (x ma x) non-zero predetermined value to which a characteristic amplitude of the vibrations in forced sinusoidal mode of the vibrating element (15) in the direction of the pilot mode (x) must be controlled; and - the simultaneous implementation of the first force (F x) on the vibrating element (15) and the control of the characteristic amplitude of the vibrations in forced sinusoidal mode of the vibrating element (15) in the direction (x) of the pilot mode by means of the first control module (20) receiving measurements of the vibrations of the vibrating element (15) in the direction (x) of the pilot mode from a measurement module (30) of the vibrations of the vibrating element (15); the method being characterized in that it further comprises: - supplying to a second servo module (25): c) a second amplitude (F y , ma x) of a second force (F y ) to be exerted in phase quadrature with the first force along the direction of the detection mode (y), and d) a detection amplitude (y ma x) non-zero predetermined value to which a characteristic amplitude of the vibrations of the vibrating element (15) in the direction (y) of the detection mode must be controlled; and - the simultaneous implementation of the second force (F y ) on the vibrating element (15) and the control of the characteristic amplitude of the vibrations of the vibrating element (15) in the direction (y) of the detection mode by means of the second control module (25) receiving measurements of a position of the vibrating element (15) in the direction (y) of the detection mode from the measuring module (30); and - determining, by means of a determination module (35) of the sensor, an instantaneous angular velocity (Q(t)) of the housing in an inertial frame of reference from the first and second amplitudes (F x , max , F y , ma x) of the first and second forces (F x , F y ), pilot amplitudes (x max ) and detection (y max ) non-zero, as well as measures of the vibrations of the vibrating element (15) transmitted by the measuring module (30) to the first and second servo modules (20, 25).

2. A method (400) according to any preceding claim, wherein the ratio of the pilot amplitude (x max ) and the detection amplitude (y max ) is less than 100.

3. Method according to any one of the preceding claims, in which the vibrations of the vibrating element are characterized by a pulsation (eu) different from the proper pulsation (wo, x , wo, y ) of the vibrating element, the relative difference between the pulsation (co) and the proper pulsation (coo.x, wo, y ) being less than 10%, preferably of the order of 1% or less.

4. Method according to any one of the preceding claims, further comprising a step of determining a pulsation (co) characteristic of the vibrations of the vibrating element (15) by means of the determination module (35), from the measurements of the positions of the vibrating element (15) transmitted by the measurement module (30) to the first and second servo modules (20, 25).

5. Method according to any one of the preceding claims, in which the implementation of the first force (F x ) and the second force (F y ) on the vibrating element (15) comprises a step of determining a matrix characteristic of an anisotropy of the vibrating element (15) from an amplitude of a third force (F x , am P , max) and an amplitude of a fourth force (F y ,am P,max) actually exerted by respectively the first servo module (20) and the second servo module (25) to respectively control the characteristic amplitude of the vibrations of the vibrating element (15) in the direction (x) of the pilot mode and the characteristic amplitude of the vibrations of the vibrating element (15) in the direction (y) of the detection mode.

6. Gyroscopic sensor (10) 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 measurement module (30) capable of generating measurements of the vibrations of the vibrating element (15) along the directions (x,y) of the pilot mode and the detection mode; - a first servo module (20) capable of: i) exerting a first force (F x ), whose amplitude is equal to a first amplitude (Fx, max ) predetermined, on the vibrating element (15) in the direction (x) of the pilot mode, ii) simultaneously controlling a characteristic amplitude of vibrations of the vibrating element (15) in forced sinusoidal mode along the direction (x) of the pilot mode to a pilot amplitude (x ma x) non-zero predetermined, iii) receiving measurements of the vibrations of the vibrating element (15) in the direction of the pilot mode (x) from the measuring module (30) to carry out this control; the sensor (10) being characterized in that it comprises: - a second servo module (25) capable of: iv) exerting a second force (F y ), whose amplitude is equal to a second amplitude (F y , max) predetermined, on the vibrating element (15) in the direction of the detection mode (y), the second force (F y ) being in phase quadrature with the first force (F x ), v) simultaneously controlling a characteristic amplitude of the vibrations of the vibrating element in the direction (y) of the detection mode to a detection amplitude (y ma x) non-zero, vi) receiving measurements of the vibrations of the vibrating element (15) along the direction (y) of the detection mode from the measuring module (30) to carry out this control; and - a determination module (35) capable of determining an instantaneous angular velocity (Q(t)) of the housing (12) in an inertial frame of reference from the amplitudes (Fx.max, F y ,max) of the first force (F x ) and the second force (F y ), the non-zero pilot amplitude (Xmax) and the detection amplitude (y max) non-zero, as 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).

7. Computer program comprising instructions which cause the sensor (10) according to claim 6 to execute the step of determining (420) the instantaneous angular velocity (O(t)) of the housing (12) of the method (400) according to any one of claims 1 to 5.

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