Measuring method and gyroscopic sensor

Abstract

Method of measurement and gyroscopic sensor The present invention relates to a 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) comprising the supply to a first servo module (20) of a first force (Fx) to be exerted in the direction of the pilot mode (x) on the vibrating element (15), and of a pilot amplitude (xmax) of servoing the vibrations in the direction of the pilot mode (x); the simultaneous implementation of the first force (Fx) and the servoing of the vibrating element (15) in the direction (x) of the pilot mode; supplying to a second servo module (25) a second force (Fy) to be exerted in phase quadrature with the first force along the direction of the detection mode (y), and a non-zero detection amplitude (ymax) for servoing the vibrations along the direction (y) of the detection mode;the simultaneous implementation of the second force (Fy) and the servo-control following the direction (y) of the detection mode; and the determination of an instantaneous angular velocity (Ω(t)) of the housing in an inertial frame of reference. Figure for the abstract: 2;

Description

Title of the invention: Measuring method and gyroscopic sensor

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

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

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

[0004] The CVG therefore comprises 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 which is exerted on the vibrating element.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0019] However, this is very unlikely, because the sources of errors are numerous and 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 of the electronic cards which coordinate the implementation of the gyroscopic measurement process.

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

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

[0022] Furthermore, the control signal used in FR 2937414 must make it possible to return to the same angular position between the start and the end of the control period. In cases where the gyroscope is moving in the inertial frame of reference and not at rest, such a signal will not make it possible to have a zero-mean control signal and to return to the same angular position at the same time.

[0023] An aim of the invention is then to propose a gyroscopic measurement method 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.

[0024] To this end, the invention relates to a method of gyroscopic measurement by means of a sensor comprising a housing and a vibrating element capable of vibrating relative to the housing in a vibration plane simultaneously in a direction of a pilot mode and in a direction of a detection mode different from the direction of the pilot mode, the method comprising: - the supply to a first sensor control module: 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 controlled; and - 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: - 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 in the direction of the detection mode must be controlled; and - 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 - 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.

[0025] 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.

[0026] 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.

[0027] The control of the amplitude of the vibrations according to the detection mode to a non-zero value is carried out by the implementation of a force following 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 amplitude of the vibrations 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.

[0028] According to other advantageous aspects of the invention, the measuring method comprises one or more of the following characteristics, taken in isolation or in all technically possible combinations:

[0029] - the ratio of the pilot amplitude and the detection amplitude is less than 100;

[0030] - 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;

[0031] - the method further comprises a step of determining a characteristic pulsation vibration characteristics 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.

[0032] - 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.

[0033] The invention also relates to a gyroscopic sensor comprising: - a case; - a vibrating element capable of vibrating relative to the housing in a vibration plane simultaneously in a direction of a pilot mode and in a direction of a detection mode different from the direction of the pilot mode; - a 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; - a first servo 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 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) receive measurements of the vibrations of the vibrating element following the direction of the pilot mode from the measurement module to carry out this control; the sensor being characterized in that it comprises: - a second servo 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 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 measuring module to carry out this control; and - 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 measuring module to the first and second control modules.

[0034] The invention also relates to a computer program comprising instructions which cause the sensor as described above to execute the step of determining the instantaneous angular velocity of the housing of the method according to any one of the preceding embodiments.

[0035] 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:

[0036] [Fig-1] [Fig.l] is a schematic representation of a CVG according to the invention;

[0037] [Fig.2] [Fig.2] Part A is a schematic representation of the operation of the CVG of the prior art; [Fig.2] part B is a schematic representation of the operation of the CVG of [Fig.l];

[0038] [Fig.3] [Fig.3] is a schematic representation of the trajectory of the element vibrating from [Fig.l] and the directions of its pilot and detection modes in a space frame linked to the housing;

[0039] [Fig.4] [Fig.4] is a flowchart representation of a process according to the invention.

[0040] The Coriolis effect gyroscopic sensor 10, designated by the abbreviation CVG in the following, according to the invention is described with reference to [Fig.l].

[0041] The CVG 10 comprises a housing 12 and a vibrating element 15 capable of vibrating relative to the housing 12.

[0042] 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.

[0043] Three axes X, Y, Z of the XYZ space frame of a reference frame linked to the housing 12 are represented in [Fig.l], the Z axis being of fixed direction in a space frame of an inertial reference frame.

[0044] 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.

[0045] To this end, the vibrating element 15 is capable of vibrating in the XY plane along two di- x and y directions, with a specific pulsation co, respectively co.

[0046] 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.

[0047] The CVG 10 comprises a first servo module 20 capable of servo-controlling a characteristic vibration amplitude of the vibrating element 15 to a predetermined non-zero pilot amplitude x max, the vibrating element 15 vibrating in a sinusoidal regime forced to 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.

[0048] 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.

[0049] As an example, which will be called a reference example hereinafter, the first servo module 20 comprises an electrostatic device 20A configured to exert on the vibrating element 15 a first force Fxamp in the direction x of the pilot mode. The first force Fx>amp is then proportional to a first amplitude command.

[0050] 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.

[0051] The first servo module 20 is capable of receiving a first predetermined amplitude F x,max of a second force Fx and of exerting this second force on the vibrating element 15 in the x direction of the pilot mode.

[0052] In the example described above, the electrostatic device 20A is thus configured to exert the second force Fx in the direction x of the pilot mode and of amplitude Fxmax. The second force Fx is then proportional to a stiffness command, which is sent by the processor or the programmable logic circuit and injected into the electrostatic device 20A by means of the proximity card.

[0053] The processor or the programmable logic circuit is advantageously configured to manage the control of the pulsation of the vibrations of the vibrating element 15 according to the direction x of the pilot mode.

[0054] As will be seen later, the second force Fx, of predetermined amplitude Fxmax, is different from the first force Fxamp which is intended to combat the damping of the vibrations of the vibrating element 15 in the direction x of the pilot mode to maintain constant the amplitude of the vibrations in the direction x of the pilot mode.

[0055] The first servo module 20 is therefore configured to exert on the vibrating element 15 a total force Ftot x along the direction x of the pilot mode which is the resultant of the first force Fx>ampet of the second force Fx, the control of the amplitude of the vibrations of the vibrating element 15 along the direction x of the pilot mode being carried out in the presence of the second force Fx.

[0056] The CVG 10 comprises a second servo-control 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 non-zero detection amplitude ymax, the vibrating element 15 vibrating in a forced sinusoidal regime along the direction y of the detection mode at a pulsation co, from measurement data of the position of the vibrating element along the direction y of the detection mode.

[0057] To this end, the second servo module 25 comprises servo means similar to those of the first servo module 20 (not shown in detail).

[0058] Thus, in the reference example, the second servo module 25 comprises an electrostatic device 25A configured to exert on the vibrating element 15 a third force Fy>amp in the direction y of the detection mode. The third force Fy>amp is then proportional to a second amplitude command.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] The third force Fy>amp is intended to maintain the amplitude of the vibrations along the y direction of the detection mode equal to the non-zero detection amplitude ymax. It is therefore different from the force exerted in the prior art along 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 along the detection mode.

[0064] The second servo module 25 is capable of receiving a second amplitude Fy>max of a fourth force Fy to be exerted on the vibrating element 15 in the y direction of the detection mode.

[0065] In the reference example, the electrostatic device 25A is thus configured to exert a fourth force Fy in the direction y of the detection mode and of amplitude the second amplitude Fy max. The fourth force Fy 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.

[0066] As will be seen later, the fourth force Fy, of predetermined amplitude Fymax, is different from the third force Fy>amp which is intended to combat the damping of the vibrations of the vibrating element 15 in the direction y of the detection mode to maintain constant the amplitude of the vibrations in the direction y of the detection mode.

[0067] The second servo module 25 is therefore configured to exert on the vibrating element 15 a total force Ftot>y along the direction y of the pilot mode which is the resultant of the third force Fy>ampet of the fourth force Fy, the servo-control of the amplitude of the vibrations along the direction y of the detection mode thus being carried out in the presence of the third force.

[0068] 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.

[0069] In particular, the measuring module 30 is capable of measuring the position x(t) (respectively y(t)) of the vibrating element 15 and / or its speed dx / dt(t) (respectively dy / dt(t)) and / or its acceleration d2x / dt2(t) (respectively d2y / dt2(t)) along the x direction (respectively along the y direction).

[0070] 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.

[0071] 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.

[0072] The measurement module 30 is also configured to exchange information with a determination module 35 of the CVG 10.

[0073] 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.

[0074] The determination module 35 is capable of determining an angular speed ins- tantanate Q(t) of box 12 at a date t in the inertial frame from: - measurements of the vibrations of the vibrating element 15 generated by the measuring module 30, - of the first amplitude Fx>max, - of the second amplitude Fy>max, - of the non-zero pilot amplitude xmax, - and the non-zero detection amplitude ymax.

[0075] Advantageously, the determination module 35 is capable of determining a co-pulsation characteristic of the vibrations of the vibrating element 15 according to the pilot mode and / or respectively according to the detection mode.

[0076] 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.

[0077] The gyroscopic measurement method 400 implemented by means of the CVG 10 will now be described with reference to [Fig.2] part B and to [Fig.4].

[0078] 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 Kx and Ky, as shown in [Fig.l]

[0079] Furthermore, it is considered in the following that the stiffness constants and the natural pulsations of the vibrating element 15 are identical according to the pilot mode x and the mode y. In this particular case, it can therefore be written that Kx= Ky= K and that co0x = (¾ = «o-

[0080] This simplification should in no case be considered as limiting for the operation of the sensor according to the invention, the following equations being able to be rewritten without difficulty in the most general case.

[0081] The method 400 comprises: - a forcing step 410 comprising the simultaneous exertion of the second force Fx by means of the first servo module 20 and of the fourth force Fy by means of the second servo module 25, the amplitudes of the vibrations of the vibrating element being simultaneously slaved respectively to the non-zero pilot amplitude x max and to the non-zero detection amplitude ymax, - followed by a step 420 of determining the instantaneous angular speed Q(t) of the box 12 in the inertial frame of reference.

[0082] In the forcing step 410, the mass M is excited so as to vibrate in a forced sinusoidal regime at the pulsation co along the direction x with the non-zero amplitude xmax, while the second force Fx is exerted on the mass M in the direction x of the pilot mode.

[0083] For this, the first servo module 20 receives from the module 30 measures the vibrations of the mass M along the x direction of the pilot mode and exerts the first force Fxamp.

[0084] The first servo module 20 thus simultaneously exerts the second force Fx and the first force Fx>amp which is configured to maintain constant the amplitude of the vibrations of the vibrating element 15 in the direction x.

[0085] The first and second forces are in phase quadrature with each other and of co-pulsation.

[0086] 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 Ftot>x, which is the resultant of the second force Fx and the first force Fx>amp.

[0087] 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 direction x of the pilot mode, while the fourth force Fy is exerted on the vibrating element 15.

[0088] 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 Fy>amp on the mass M. The third force Fy>amp has the direction y of the detection mode and is in phase quadrature with the first force Fxamp.

[0089] The second servo module 25 thus simultaneously exerts the fourth force Fy and the third force Fy>amp configured to maintain constant the amplitude of the vibrations of the vibrating element 15 in the direction y.

[0090] The third and fourth forces Fy amp and Fy are in quadrature with each other, and the fourth force is in phase quadrature with the second force Fx.

[0091] 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 Ftot>y, which is the resultant of the fourth force Fy and the third force Fy>amp.

[0092] 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 co along the x direction with the non-zero amplitude xmax as in the methods of the prior art, as well as, along the y direction with the non-zero amplitude ymax, 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 co as according to the pilot mode but in phase quadrature.

[0093] In the method 400, the mass M is therefore simultaneously excited simultaneously along the x direction by a second force of the form Fx = Fx>maxcos (eut) and along the y direction by a fourth quadrature force, of the form Fy = Fy>maxsin (eut) in above the first force Fx>amp and the third force Fy>amp intended to control the amplitudes of the vibrations according to the pilot and detection modes.

[0094] It will be shown later that during the forcing step 410, due to the presence of the second force Fx and the fourth force Fy, the vibrating element 15 vibrates at a pulsation co different from but close to the natural pulsation co0.

[0095] If, in a step prior to the forcing step 410, the vibrating element is excited at its own pulsation co0 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 co0 to the pulsation co will occur spontaneously during a transient phase at the start of the forcing step 410.

[0096] In the determination step 420, the determination module 35 determines the instantaneous angular velocity Q(t) in the inertial frame of reference.

[0097] The determination module 35 receives for this: - measurement results of the vibrations of the vibrating element 15 from the measuring module 30, - the amplitude Fx>max of the first force and the amplitude Fy>max of the second force, - as well as the amplitudes xmax and ymax.

[0098] 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.

[0099] The model for determining the instantaneous angular velocity Q(t) may include explicit equations based on the fundamental principle of dynamics.

[0100] 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) = xmaxcos (eut) and the position y of the mass M along the direction y of the detection mode as a function of the date t is of the form y(t) = ymaxsin (eut).

[0101] The trajectory of the mass M is therefore an ellipse in the xyZ reference frame, unlike the methods of the prior art for which the trajectory of the mass M is a straight line segment in direction x.

[0102] If the direction x of the pilot mode relative to the X axis of the XYZ reference frame linked to the housing 12 is identified by the angle 0 represented in [Fig.3], the coordinates X and Y of the mass m in the XYZ reference frame linked to the housing 12 are linked to the coordinates x and y of the mass M in the xyZ reference frame by equation 1:

[0103] [Math.l] -sinB YJL sinf) cosf)

[0104] with [y]=R(fl)[y [Math.2] ' cos3 . sinO -sind' cos 3 .

[0105]

[0106]

[0107]

[0108]

[0109]

[0110] [YES]

[0112]

[0113]

[0114] The first time derivatives dX / dt and dY / dt of the X and Y coordinates of the mass M therefore verify: [Math.3] / U x-3s ' \ / [dx + ÿ The second time derivatives d2X / dt2 and d2Y / dt2 of the X and Y coordinates of the mass M verify: [Math.4] = R KJ U x-32x-23y-3y ' .. .7 / [ 2 / Zx+ 3x+ÿ- 3 y _ 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: [Math.5] Ÿ] / \[ x-23y y] \ / [20x+ÿ. In the frame of reference of the box 12, the mass M is subjected during the forcing step 410 to the first force Fx>amp, to the second force Fx, to the third force Fy>amp, to the fourth force Fy, to the restoring forces of the springs, as well as to damping which is modeled by a fluid friction force along each of the directions x and y associated with a quality factor Q. The damping matrix A of the vibrating element 15, taking into account damping anisotropies, is of the form described in equation 6: [Math.6] a - 1 01 [ al a2 ' Q '10 11 La2 -al. The stiffness matrix Kl of the vibrating element 15, taking into account anisotropies of stiffness, is of the form: [Math.7] r2 „ 0 rl r2 r2 1 - rl J Furthermore, when the frame of reference of the box 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 box 12, is subjected to a Coriolis inertial force in this frame of reference of the box 12.

[0115] 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:

[0116] [Math. 8] ,JX] „ [X] JX] or.[0 -M][X] n / Jf* + FW m +^i „ . +2Q „ -Rie) \ = R(e\ [y] m [y] lm o J[yj [^;y] 4¾] [ / -, + 0,,,,,,.

[0117] or, after multiplication by R(-0) and with the approximations of equation 5:

[0118] [Math.9] 'JW-IKfc

[0119] The left-hand side of the equation shows an anisotropy term of amortization of the form:

[0120] [Math. 10] d / Z [al «2 ] \ [X] \ y L«2 -Æ1J / J

[0121] whose component ax following the direction of the pilot mode x is:

[0122] [Math. 11] ax= (^p+alcos(20)+a2sin(20))x+(a2cos(20)-alsin(20))y =a^ x + y

[0123] and whose component ay following the direction of the detection mode y is worth:

[0124] [Math. 12] ax = (“2cos(20) - a lsin(20))X + - alcos(20) - û2sin (20)) y =aIv. .1+¾ ;y = (^- x-ai..t.i'

[0125] The first term aijXdx / dt of the component ax of the anisotropy term damping, i.e. the term proportional to dx / dt, is compensated by means of the first force Fx>amp. It is therefore compensated in the reference example by means of the first amplitude command of the first servo module 20.

[0126] The second term a2jXdy / dt of the ax component of the damping anisotropy term, which is proportional to dy / dt, is compensated by means of the second force Fx. It is therefore compensated in the reference example by means of the stiffness control of the first servo module 20.

[0127] The first force Fxampa therefore for expression

[0128] [Math. 13] FXM-fFtp — ( + aIcos (20) + d2sin(20) )x

[0129] The second term a2>ydy / dt of the component ay of the damping anisotropy term, i.e. the term proportional to dy / dt, is observable precisely because the amplitude of vibrations along the direction of the detection mode is fixed at a non-zero value ymax.

[0130] It is compensated by means of the third force Fy>amp, therefore in the example described above by means of the second amplitude control of the second module of enslavement 25.

[0131] The third force Fy>ampa therefore for expression

[0132] [Math. 14] Fy^mp = ( -yp - a Icos ( 26* ) - r / 2si n ( 26* ) jy

[0133] We see that the third force Fy>amp is proportional to dy / dt and therefore only exists because the movement of the vibrating element in the xyZ frame is elliptical and not rectilinear. The third force Fy>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.

[0134] We also note that the amplitudes Fx>amp>max and Fy>amp max of the first and third forces verify

[0135] [Math. 15] alcos(20) + «2sin(20) =

[0136] 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.

[0137] The coefficients a1 and a2 can in particular be deduced from equation 15 as soon as measurements are available for several different angles 0.

[0138] 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 Mco0 / 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.

[0139] 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 Fxamp and the third force Fy>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.

[0140] In the end, if we neglect the harmonic errors linked to the stiffness anisotropies (corresponding to the terms rl 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:

[0141] [Math. 16] -x™« «2)-2^a -alsin(2«))«>ym <i(

[0142] where Fx>max is the first amplitude, i.e. the amplitude of the second force Fx to be supplied to the first servo module 20, and

[0143] [Math. 17] -2éxmaxw-2Qœxmax-fa^

[0144] where Fy>max is the second amplitude, i.e. the amplitude of the fourth force Fy to be supplied to the second servo module 25.

[0145] In the methods of the prior art, the excitation pulsation co is approximately equal to the natural pulsation co0 and ymax = 0.

[0146] On the contrary, in the method 400 according to the invention, the amplitude ymax is fixed and equal to a non-zero predetermined value, as is the amplitude xmax.

[0147] Furthermore, we have seen that the coefficients of the anisotropy matrix are precisely determined from the third force Fy>amp.

[0148] These coefficients make it possible to correct in real time the anisotropy defects appearing in equations 16 and 17, so that ultimately, the second and fourth forces have the following expression after correction in real time by the control modules 20, 25 of the anisotropy defects made accessible:

[0149] = x (œ2. W2) _2^v w-2Qw

[0150] [Math. 19] ~ y (^o- ~ 2dxmaxœ - 2ilujxmax

[0151] The anisotropy errors are therefore known and managed in the method 400, unlike the methods of the prior art.

[0152] In the method 400 according to the invention, it is understood with equations 18 and 19 that the angle 0 which characterizes the direction x in the XY reference 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:

[0153] [Math.20] to — O _>__1............. / % 1 Q y ]

[0154] 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.

[0155] 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 dO / dt, from the first amplitude Fx>max, from the second amplitude Fy>max, as well as from the amplitudes x max and ymax and from the following equation 21:

[0156] [Math.21] Qf t ] _ _ a .__I_____ / £2221 _ ?r \ L / “ ut [ ^max MœQ j

[0157] 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.

[0158] As previously indicated, the pulsation co is close to the proper pulsation cüo of the vibrating element, so is an estimator of this proper pulsation, which can be injected into equation 21 to determine the instantaneous angular velocity Q(t).

[0159] Equations 18 and 19 in fact make it possible to form the following equation 22 on the co pulsation:

[0160] [Math.22] w + 2ymax~ï^ Jw wo

[0161] It will further be noted that it is possible to adjust one and / or the other of the predetermined amplitudes Fx>max and Fy>max to increase or reduce the pulsation slip relative to the natural pulsation co0-

[0162] Advantageously, the relative difference between the pulsation co and the natural pulsation cüo is less than 10%, preferably of the order of 1% or less.

[0163] Typically, the natural pulsation can be of the order of 10 Hz. The relative difference between the co pulsation and the natural cooper pulsation can then be less than 1 Hz, and in particular typically be of the order of a tenth of Hz.

[0164] To the extent that the implementation of vibrations of non-zero amplitude 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 ani-sotropies permitted by the non-zero detection amplitude ymax and these new errors.

[0165] Advantageously, the ratio of the pilot amplitude xmax and the detection amplitude Ymax is less than 10, or even less than 100.

[0166] Advantageously, the detection amplitude ymax is of the order of 1 / 100th, or even of the order of 1 / 1000th 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 (Fx>max) of a first force (Fx) to be exerted in the direction of the pilot mode (x) on the vibrating element (15), and b) a predetermined non-zero pilot amplitude (xmax) 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 servo-controlled; and - the simultaneous implementation of the first force (Fx) 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 (Fy>max) of a second force (Fy) to be exerted in phase quadrature with the first force along the direction of the detection mode (y), and d) a predetermined non-zero detection amplitude (ymax) to which a characteristic amplitude of the vibrations of the vibrating element (15) along the direction (y) of the detection mode must be servo-controlled; and - the simultaneous implementation of the second force (Fy) 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 measurement module (30); and - the determination, by means of a determination module (35) of the sensor, of an instantaneous angular velocity (Q(t)) of the housing in an inertial frame of reference from the first and second amplitudes (Fx>max, Fy >max) of the first and second forces (Fx, Fy), the non-zero pilot (xmax) and detection (ymax) amplitudes, 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).

2. A method (400) according to any preceding claim, wherein the ratio of the pilot amplitude (xmax) and the detection amplitude (ymax) 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 (œ) different from the proper pulsation (co0jX, co0>y) of the vibrating element, the relative deviation between the pulsation (œ) and the proper pulsation (co0jX, coo>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 (œ) 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 (Fx) and the second force (Fy) on the vibrating element (15) comprises a step of determining a characteristic matrix of an anisotropy of the vibrating element (15) from an amplitude of a third force (Fxampmax) and an amplitude of a fourth force (Fy>amp>max) actually exerted by respectively the first servo module (20) and the second servo module (25) to respectively servo the characteristic amplitude of the vibrations of the vibrating element (15) along the direction (x) of the pilot mode and the characteristic amplitude of the vibrations of the vibrating element (15) along 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;

7. - 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 (Fx), the amplitude of which is equal to a first predetermined amplitude (Fxmax), 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 predetermined non-zero pilot amplitude (xmax), iii) receiving measurements of the vibrations of the vibrating element (15) along the direction of the pilot mode (x) from the measurement 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 (Fy), the amplitude of which is equal to a second predetermined amplitude (Fy>max), on the vibrating element (15) in the direction of the detection mode (y), the second force (Fy) being in phase quadrature with the first force (Fx), v) simultaneously controlling a characteristic amplitude of the vibrations of the vibrating element in the direction (y) of the detection mode to a non-zero detection amplitude (ymax), 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, Fy>max) of the first force (Fx) and of the second force (Fy), of the non-zero pilot amplitude (xmax) and of the non-zero detection amplitude (ymax), 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). Computer program comprising instructions which cause the sensor (10) according to claim 6 to execute the step of determining (420) the instantaneous angular velocity (Q(t)) of the housing (12) of the method (400) according to any one of claims 1 to 5.

Images