Measurement method and gyroscopic sensor
The gyroscopic measurement method addresses intrinsic errors by controlling and evaluating damping anisotropy through forces in quadrature phase, enhancing angular velocity measurement precision.
Patent Information
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2024-03-25
- Publication Date
- 2026-04-10
AI Technical Summary
Existing gyroscopic measurement methods suffer from intrinsic errors due to anisotropies, damping defects, excitation control electronics issues, and position detection errors, which are not accurately evaluated and compensated, leading to inaccurate angular velocity measurements, especially when the sensor is in motion.
A gyroscopic measurement method that applies forces in quadrature phase along both pilot and detection modes to control and evaluate damping anisotropy errors, using a gyroscopic sensor with servo modules to maintain non-zero amplitudes in both directions, allowing for precise estimation and compensation of these errors.
The method improves measurement accuracy by quantitatively accounting for anisotropy errors, resulting in more precise determination of instantaneous angular velocity, even when the sensor is in motion.
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Abstract
Description
Title of the invention: Gyroscopic measurement method and sensor
[0001] The present invention relates to a gyroscopic measurement method.
[0002] The invention also relates to a gyroscopic sensor for implementing the gyroscopic measurement method, as well as a computer program comprising instructions that lead the sensor to perform the step of determining the instantaneous angular velocity of the gyroscopic sensor of this method.
[0003] A Coriolis Vibratory Gyroscope (CVG) sensor allows measurement of the component along an axis, called the sensitivity axis, of an instantaneous rotation velocity vector of a reference frame attached to a sensor housing with respect to an inertial reference frame.
[0004] The CVG comprises for this purpose a vibrating element of the sensor capable of vibrating relative to the housing. The measurement is carried out by means of the effects of the Coriolis inertial force exerted on the vibrating element.
[0005] The vibrating element of a CVG is capable of vibrating along two coplanar vibration directions, called the pilot mode direction and the detection mode direction, the work of the Coriolis force allowing a transfer of mechanical energy between the two directions.
[0006] The sensitivity axis of the CVG is orthogonal to the plane of the directions of the pilot mode and the detection mode.
[0007] For the measurements, the vibrating element is excited along the pilot mode direction at its resonant frequency by the excitation system. The amplitude of the vibrations along the pilot mode is kept constant by means of a feedback control system for the voltage applied to the excitation system. Any variations in the resonant frequency, particularly those related to variations in the temperature of the vibrating element, are monitored by means of a frequency feedback control system.
[0008] If the component along the sensitivity axis of the instantaneous rotational velocity vector of the housing with respect to an inertial reference frame is non-zero, the displacement of the vibrating element along the pilot mode direction generates a Coriolis force. This force excites the vibrating element along the detection mode direction, with an amplitude that is proportional to the component along the sensitivity axis of the instantaneous rotational velocity vector.
[0009] A CVG can operate in two modes: gyroscope mode and gyrometer mode.
[0010] In gyroscope mode, the position of the pilot mode direction in the vibration plane is free. The instantaneous rotational speed to be measured is then deduced from the angular position of the vibration plane of the vibrating element in the reference frame attached to the housing.
[0011] In gyroscope mode, the direction of the pilot mode in the plane of vibration is controlled by sending an electronic command and the instantaneous rotation speed to be measured is deduced from the force to be exerted to control this direction.
[0012] Whether the CVG is used in gyroscope mode or gyrometer mode, the measurements are affected by intrinsic errors related to defects in the CVG. Among these defects, we can mention the anisotropies of stiffness or damping of the vibrating element, defects in the excitation control electronics or the position detection electronics of the vibrating element, defects in the electrical reference voltage for the excitation, etc.
[0013] Among these errors, some are called harmonic because they are proportional to cosine or sine functions of an angle that is an even multiple of the angle characterizing the position of the directions of the pilot mode and the detection mode in the reference frame linked to the housing.
[0014] US 6 598 455 describes a method of gyroscopic measurements in which the geometric vibration position of the gyroscope is intentionally modified by electrostatic means over time, in order to improve the calibration of the gyroscope.
[0015] US 7 093 370 further describes a MEMS gyroscope in which an angular velocity is intentionally imposed on the sensor by mechanical means, the direction of rotation of the sensor being periodically alternated in order to reduce measurement errors and in particular scaling factor errors of the gyroscope.
[0016] FR 2937414 describes a vibrating gyroscope that combines the principles of US patent 6,598,455 by injecting an electronic signal to rotate the vibration wave and US patent 7,093,370 by imposing a periodically alternating electrical rotation to minimize harmonic errors. The control signal is adapted to rotate the geometric vibration position of the gyroscope in one direction for a portion of the control signal period according to a first velocity profile, and then in the opposite direction according to a second velocity profile. The vibrating gyroscope then provides a corrected signal based on the difference between the measurement signal and the control signal.
[0017] However, due to errors in the chain converting the control signal into an electrostatic force, the force actually applied to the vibrating element of the gyroscope to obtain its alternating rotation is different from the force that should theoretically be obtained from the control signal.
[0018] If the errors of the conversion chain are perfectly stable over time, the error made on the angle measurement can be zero over a period characteristic of the variations of the control signal.
[0019] However, this is very unlikely, as the sources of error are numerous and of different kinds. We can mention in particular the detection errors of the detection combs, the excitation errors of the excitation combs as well as the instabilities of the reference voltage used for the operation of these combs, and the errors of the electronic boards which coordinate the implementation of the gyroscopic measurement process.
[0020] Ultimately, in most situations, the average value of the error is not zero over a period of the alternating rotation of the sensor's position. Furthermore, during the round trip of the wave, the angular errors of the sensor are greater the more significant the aforementioned defects are.
[0021] Such a device reduces the impact of defects on the measurement without allowing the measurement error related to these defects to be evaluated.
[0022] Furthermore, the control signal used in FR 2937414 must allow the gyroscope to return to the same angular position between the beginning and end of the control period. In cases where the gyroscope is moving in the inertial frame of reference and not at rest, such a signal will not allow both a zero-average control signal and a return to the same angular position.
[0023] One object of the invention is then to propose a gyroscopic measurement method allowing to estimate certain measurement errors, in particular harmonic anisotropy errors, in order to take them into account in the result of the measurement, and thus to obtain a measurement result of known, or even improved, precision, regardless of the nature of the movement of the sensor in an inertial frame of reference.
[0024] To this end, the invention relates to a gyroscopic measurement method using a sensor comprising a housing and a vibrating element capable of vibrating relative to the housing in a plane of vibration simultaneously along a pilot mode direction and along a detection mode direction different from the pilot mode direction, the method comprising: - the supply to a first sensor control module: a) of a first amplitude of a first force to be exerted along 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 regime of the vibrating element along 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 regime of the vibrating element along the direction of the pilot mode by means of the first control module receiving measurements of the vibrations of the vibrating element along the direction of the pilot mode from a vibration measurement module of the vibrating element; the process being characterized in that it further comprises: - supplying to a second control module: c) a second amplitude of a second force to be exerted in quadrature phase 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 - the simultaneous application 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 - the determination, by means of a sensor determination module, of an instantaneous angular velocity of the housing in an inertial reference frame from the first and second amplitudes of the first and second forces, the non-zero pilot and detection amplitudes, as well as the 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 servo system.
[0026] The vibrating element oscillates with a non-zero amplitude along the direction of the pilot mode, as in 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 vibration amplitude according to the detection mode to a non-zero value is achieved by applying a force along the direction of the detection mode. Evaluating this force, in combination with evaluating the force actually applied to control the vibration amplitude according to the pilot mode, allows for the estimation of the damping anisotropy errors of the vibrating element. These estimated errors can then be quantitatively taken into account in the step of determining the angular velocity of the housing. Thus, the accuracy of the gyroscopic measurement is improved compared to prior art methods, in which these errors are minimized but not evaluated.
[0028] According to other advantageous aspects of the invention, the measurement method comprises one or more of the following features, taken individually 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 on the order of 1% or less;
[0031] - the method further comprises a step of determining a characteristic pulse Vibration measurement of the vibrating element using the determination module, based on measurements of the positions of the vibrating element transmitted by the measurement module to the first and second control modules.
[0032] - the application of the first force and the second force on the vibrating element includes 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 control module and the second control module to control respectively the characteristic amplitude of the vibrations of the vibrating element along the direction of the pilot mode and the characteristic amplitude of the vibrations of the vibrating element along 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 plane of vibration simultaneously along a direction of a pilot mode and along a direction of a detection mode different from the direction of the pilot mode; - a measurement module capable of generating vibration measurements of the vibrating element according to the directions of the pilot mode and the detection mode; - a first servo module capable of: i) exert 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 control a characteristic vibration amplitude of the vibrating element in a forced sinusoidal regime along the direction of the pilot mode to a predetermined non-zero pilot amplitude, iii) receive measurements of the vibrations of the vibrating element along the direction of the pilot mode from the measurement module to achieve this control; the sensor being characterized in that it comprises: - a second control module capable of: (iv) exert 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 quadrature phase with the first force, (v) simultaneously control a characteristic amplitude of the vibrations of the vibrating element along the direction of the detection mode to a non-zero detection amplitude, vi) receive measurements of the vibrations of the vibrating element along the direction of the detection mode from the measurement module to achieve this control; and - a determination module capable of determining an instantaneous angular velocity of the housing in an inertial reference frame 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 control modules.
[0034] The invention also relates to a computer program comprising instructions which lead the sensor as described above to perform the step of determining the instantaneous angular velocity of the process housing according to any one of the preceding embodiments.
[0035] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the drawings in which:
[0036] [Fig-1] [Fig.1] is a schematic representation of a CVG according to the invention;
[0037] [Fig.2] Part A of [Fig.2] 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.1];
[0038] [Fig.3] [Fig.3] is a schematic representation of the trajectory of the element vibrating from the [Fig.l] and the directions of its pilot and detection modes in a spatial reference frame linked to the housing;
[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.1].
[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, implemented as a microelectromechanical system (MEMS). The vibrating element 15 and the housing 12 are then machined from a block of silicon or quartz by micromachining, and the vibrating element 15 is set into vibration by an electrical process. This arrangement minimizes the size and / or manufacturing cost of the CVG 10.
[0043] Three axes X, Y, Z of the XYZ space frame of a reference frame attached to the housing 12 are shown on [Fig.1], 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 with respect to the Z axis, which therefore constitutes the sensitivity axis of the CVG 10.
[0045] To this end, the vibrating element 15 is adapted to vibrate in the XY plane along two di- rections x and y, with a natural 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 includes a first control module 20 capable of controlling a characteristic vibration amplitude of the vibrating element 15 to a predetermined non-zero pilot amplitude x max, the vibrating element 15 vibrating in sinusoidal regime forced at 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 control module 20 includes conventional means for controlling the amplitude of the vibrations of the vibrating element 15 according to the pilot mode. These means are not shown in detail in the figures. They include, for example, the control means described in document EP2960625.
[0049] By way of example, which will be referred to as the reference example hereafter, the first servo module 20 includes 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 includes in the reference example a processor or a programmable logic circuit (such as a "Field Programmable Gate Array", FPGA), configured to manage the servo control of the first amplitude command, as well as a proximity card configured to inject the first amplitude command signal into the electrostatic device 20A.
[0051] The first servo module 20 is capable of receiving a first predetermined amplitude Fx,max of a second force Fx and of exerting this second force on the vibrating element 15 in the direction x 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 with 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 programmable logic circuit is advantageously configured to manage the control of the vibration pulse of the vibrating element 15 according to the x direction 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 counteract the damping of the vibrations of the vibrating element 15 along the direction x of the pilot mode in order to maintain constant the amplitude of the vibrations along 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 includes a second control module 25 capable of controlling a characteristic amplitude of the vibrations of the vibrating element 15 along the y direction of the detection mode to a non-zero detection amplitude ymax, the vibrating element 15 vibrating in forced sinusoidal regime along the y direction of the detection mode at a pulsation co, from measurement data of the position of the vibrating element along the y direction of the detection mode.
[0057] To this end, the second control module 25 includes control means similar to those of the first control module 20 (not shown in detail).
[0058] Thus, in the reference example, the second servo module 25 includes 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 control module 25 includes, in the reference example, a processor or a field-programmable gate array (FPGA) configured to manage the control of the second amplitude command. The second control module 25 also includes a proximity card configured to inject the second amplitude command signal into the electrostatic device 25A.
[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 but not mandatory.
[0061] The processor or programmable logic circuit is advantageously configured to manage the control of the vibration pulse of the vibrating element 15 according to the y direction of the detection mode.
[0062] The proximity card in the reference example is the same as that of the first servo module 20. This arrangement is advantageous without being mandatory.
[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 with an amplitude equal to 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 counteract the damping of the vibrations of the vibrating element 15 along the direction y of the detection mode in order to maintain constant the amplitude of the vibrations along 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 y direction 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 y direction of the detection mode being thus achieved in the presence of the third force.
[0068] The CVG 10 includes a measurement module 30 capable of generating measurements of the vibrations of the vibrating element 15 along the x directions of the pilot mode and y directions 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 velocity dx / dt(t) (respectively dy / dt(t)) and / or its acceleration d2x / dt2(t) (respectively d2y / dt2(t)) along the direction x (respectively along the direction y).
[0070] To this end, the measuring module 30 includes, in the non-limiting reference example, electrostatic detection means 30A along the x direction of the pilot mode and electrostatic detection means 30B along the y direction of the detection mode.
[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 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 control modules 20, 25.
[0074] The determination module 35 is capable of determining an angular velocity ins- tantanate Q(t) of casing 12 at a time t in the inertial frame of reference 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-characteristic pulsation 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 functions 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 using the CVG 10 will now be described with reference to [Fig.2] part B and [Fig.4].
[0078] To simplify the writing of the equations to understand this process, 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 with respective stiffnesses Kx and Ky, as shown in [Fig.1]
[0079] Furthermore, it is assumed in the following that the stiffness constants and natural frequencies of the vibrating element 15 are identical in pilot mode x and mode y. In this particular case, we can therefore write that Kx = Ky = K and that co0x = (¾ = «o-
[0080] This simplification should in no way be considered as limiting 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 process 400 comprises: - a forcing step 410 comprising the simultaneous application of the second force Fx by means of the first control module 20 and the fourth force Fy by means of the second control module 25, the amplitudes of the vibrations of the vibrating element being simultaneously controlled respectively to the non-zero pilot amplitude x max and to the non-zero detection amplitude ymax, - followed by a step of determining 420 the instantaneous angular velocity Q(t) of the housing 12 in the inertial reference frame.
[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 amplitude xmax non-zero, while the second force Fx is exerted on the mass M in the direction x of the pilot mode.
[0083] For this purpose, the first servo module 20 receives from module 30 measurements of the vibrations of 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 along the direction x.
[0085] The first and second forces are in quadrature of phase with each other and of pulsation co.
[0086] During the forcing step 410, the vibrating element 15 is therefore subjected along 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 y direction of the detection mode, with the amplitude y max non-zero and in quadrature phase with the oscillations along the x direction of the pilot mode, while the fourth force Fy is exerted on the vibrating element 15.
[0088] To do this, the second control module 25 receives from module 30 measurements of the vibrations of the mass M along the y direction of the detection mode, and it exerts the third force Fy>amp on the mass M. The third force Fy>amp has the direction of the y direction of the detection mode and is in quadrature phase 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 along the y direction.
[0090] The third and fourth forces Fy amp and Fysont 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 along the y direction 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 prior art processes, as well as, along the y direction with the non-zero amplitude ymax, unlike the prior art sensors in which the vibrating element 15 is not subjected to any forced excitation along the detection mode y, at the same pulsation co as along the pilot mode but in quadrature phase.
[0093] In the process 400, the mass M is therefore simultaneously excited 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) sus of the first force Fx>ampet of the third force Fy>ampdestined 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 different pulsation co but close to the natural pulsation co0.
[0095] If, in a step prior to the forcing step 410, the vibrating element is excited to its natural frequency 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 vibration frequency from the natural frequency co0 to the frequency co will occur spontaneously during a transient phase at the beginning 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 reference frame.
[0097] The determination module 35 receives for this purpose: - 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 time t is of the form x(t) = xmaxcos (eut) and the position y of the mass M along the direction y of the detection mode as a function of the time t is of the form y(t) = ymaxsin (eut).
[0101] The trajectory of the mass M is therefore an ellipse in the xyZ frame, unlike prior art processes for which the trajectory of the mass M is a straight line segment in the direction x.
[0102] If the x direction of the pilot mode with respect to the X axis of the XYZ frame linked to the housing 12 is located by the angle 0 shown in [Fig.3], the coordinates X and Y of the mass m in the XYZ frame linked to the housing 12 are related to the coordinates x and y of the mass M in the xyZ frame by equation 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 mass M therefore satisfy: [Math.3] / U x-3s ' \ / [dx + ÿ The second time derivatives d2X / dt2 and d2Y / dt2 of the X and Y coordinates of mass M satisfy the following: [Math.4] = R KJ U x-32x-23y-3y ' .. .7 / [ 2 / Zx+ 3x+ÿ- 3 y _ In a forced sinusoidal regime at angular frequency co, if we neglect the terms that are not proportional to a positive integer power of the angular frequency co compared to the other terms, equation 4 can be written in the simplified form of equation 5: [Math.5] Ÿ] / \[ x-23y y] \ / [20x+ÿ. In the frame of the case 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 a damping which is modeled by a fluid friction force along each of the x and y directions 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 housing 12 undergoes a rotational motion with component Q(t) along the Z direction relative to the inertial frame of reference, the mass M, due to its non-zero relative velocity in the frame of reference of the housing 12, is subjected to a Coriolis inertial force in this frame of reference of the case 12.
[0115] Applying Newton's second law to the mass M in the non-Galilean frame of reference of the casing gives 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 introduces an anisotropy term of the form's damping:
[0120] [Math. 10] d / Z [al «2 ] \ [X] \ y L«2 -Æ1J / J
[0121] whose component ax along 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 along the direction of the detection mode is:
[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 The damping term, i.e., the term proportional to dx / dt, is compensated by means of the first force Fx>amp. Therefore, in the reference example, it is compensated by means of the first amplitude control 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 has the expression
[0128] [Math. 13] FXM-fFtp — ( + aIcos (20) + d2sin(20) )x
[0129] The second term a2>ydy / dt of the component aydu damping anisotropy term, that is to say the term proportional to dy / dt, is observable precisely because the amplitude of vibrations along the direction of the detection mode is fixed to 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 25.
[0131] The third force Fy>ampa therefore has the 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 exists only because the motion of the vibrating element in the xyZ frame is elliptical and not rectilinear. The third force Fy>amp is quite different from that used in the prior art for controlling the amplitude of vibrations along the y-direction, where its value is zero.
[0134] It is further observed that the amplitudes Fx>amp>max and Fy>amp max of the first and third forces satisfy
[0135] [Math. 15] alcos(20) + «2sin(20) =
[0136] Controlling the vibration amplitudes to a non-zero value not only along the x direction but also along the y direction therefore allows the anisotropy matrix to be determined.
[0137] The coefficients al 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 irrelevant. Indeed, the term Mco0 / Q is highly dependent on the temperature of the vibrating element 15, so that it is not possible to deduce al and a2 from equation 13 alone.
[0139] In the reference example, the processor common to the first control module 20 and the second control module 25 therefore determines the first force Fxamp and the third force Fy>amp which are actually exerted by these control modules 20 and 25 to obtain the desired amplitude control along the x and y directions. It deduces from this the expression for the coefficients a1 and a2 of the anisotropy matrix.
[0140] In the end, if we neglect the harmonic errors related 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 attached to the casing 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 quadrature phase 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, that is, the amplitude of the second force Fx to be supplied to the first control module 20, and
[0143] [Math. 17] -2exmaxw-2Qœxmax-fa^
[0144] where Fy>max is the second amplitude, that is, the amplitude of the fourth force Fy to be supplied to the second control module 25.
[0145] In prior art processes, the excitation frequency co is approximately equal to the natural frequency 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 predetermined non-zero value, as is the amplitude xmax.
[0147] Moreover, we have seen that the coefficients of the anisotropy matrix are determined precisely from the third force Fy>amp.
[0148] These coefficients allow for real-time correction of the anisotropy defects appearing in equations 16 and 17, so that ultimately, the second and fourth forces have the following expression after real-time correction 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] Anisotropy errors are therefore known and managed in process 400, unlike prior art processes.
[0152] In the method 400 according to the invention, it is understood from equations 18 and 19 that the angle 0 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 satisfies 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 reference frame of the housing 12 due to the second and fourth forces applied simultaneously along these two directions.
[0155] In the determination step 420, the determination module 35 can deduce the instantaneous angular velocity Q(t) of the sensor with respect to the Z axis from the data it receives from the measurement module 30, which allows the determination of dO / dt, of the first amplitude Fx>max, of the second amplitude Fy>max, as well as of the amplitudes x max and ymax and of the following equation 21:
[0156] [Math.21] Qf t ] _ _ a .__I_____ / £2221 _ ?r \ L / “ ut [ ^max MœQ j
[0157] It should 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 stated, the pulsation co is close to the natural pulsation cüo of the vibrating element, therefore is an estimator of this natural pulsation, which can be injected into equation 21 to determine the instantaneous angular velocity Q(t).
[0159] Equations 18 and 19 can indeed be used to form the following equation 22 on the angular frequency co:
[0160] [Math.22] w + 2ymax~ï^ Jw wo
[0161] It should also 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 decrease 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 on the order of 1% or less.
[0163] Typically, the natural frequency can be on the order of 10 Hz. The relative difference between the co-frequency and the natural frequency can then be less than 1 Hz, and in particular typically be on the order of a tenth of a Hz.
[0164] Since the implementation of non-zero amplitude vibrations according to 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 allowed 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 on the order of 1 / 100th, or even on the order of 1 / 1000th of the pilot amplitude xmax.
Claims
Demands
1. A method (400) for gyroscopic measurement using a sensor (10) comprising a housing (12) and a vibrating element (15) capable of vibrating relative to the housing (12) in a vibration plane (xy) simultaneously along a direction (x) of a pilot mode and along a direction (y) of a detection mode different from the direction (x) of the pilot mode, the method comprising: - the provision to a first servo module (20) of the sensor: a) of a first amplitude (Fx>max) of a first force (Fx) to be exerted along the direction of the pilot mode (x) on the vibrating element (15), and b) of a predetermined non-zero pilot amplitude (xmax) to which a characteristic amplitude of the vibrations in forced sinusoidal regime of the vibrating element (15) along the direction of the pilot mode (x) must be servo-controlled; and - the simultaneous application of the first force (Fx) on the vibrating element (15) and the control of the characteristic amplitude of the vibrations in forced sinusoidal regime of the vibrating element (15) along 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) along 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: - the provision to a second control module (25): c) of a second amplitude (Fy>max) of a second force (Fy) to be exerted in quadrature phase with the first force along the direction of the detection mode (y), and d) of 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 controlled; and - the simultaneous application 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) along 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) along 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 reference frame from the first and second amplitudes (Fx>max, Fy >max) of the first and second forces (Fx, Fy), of 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 one of the preceding claims, wherein the ratio of the pilot amplitude (xmax) and the detection amplitude (ymax) is less than 100.
3. A method according to any one of the preceding claims, wherein the vibrations of the vibrating element are characterized by a pulsation (œ) different from the natural pulsation (co0jX, co0>y) of the vibrating element, the relative difference between the pulsation (œ) and the natural pulsation (co0jX, coo>y) being less than 10%, preferably on the order of 1% or less.
4. A 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. A method according to any one of the preceding claims, wherein 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 servo respectively 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 sensing 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 along a direction (x) of a pilot mode and along a direction (y) of a detection mode different from the direction (x) of the pilot mode;
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) exert a first force (Fx), the amplitude of which is equal to a predetermined first amplitude (Fxmax), on the vibrating element (15) in the direction (x) of the pilot mode, ii) simultaneously control a characteristic vibration amplitude of the vibrating element (15) in forced sinusoidal regime along the direction (x) of the pilot mode to a predetermined non-zero pilot amplitude (xmax), iii) receive measurements of the vibrations of the vibrating element (15) along the direction of the pilot mode (x) from the measurement module (30) to achieve 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 predetermined second amplitude (Fy>max), on the vibrating element (15) in the direction of the detection mode (y), the second force (Fy) being in quadrature phase with the first force (Fx), v) simultaneously controlling a characteristic amplitude of the vibrations of the vibrating element along the direction (y) of the detection mode to a non-zero detection amplitude (ymax), (vi) receive measurements of the vibrations of the vibrating element (15) along the direction (y) of the detection mode from the measuring module (30) to achieve 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 the second force (Fy), the non-zero pilot amplitude (xmax) and the non-zero detection amplitude (ymax), as well as from measurements of the vibrations of the vibrating element (15) transmitted by the measurement module (30) to the first and second servo modules (20, 25). A computer program comprising instructions that cause the sensor (10) according to claim 6 to perform the step of determining the instantaneous angular velocity (Q(t)) of the housing (12) of the process (400) according to any one of claims 1 to 5.