Vibration sensor with hybridization cell

Abstract

An inertial rotary sensor comprising a vibrating resonator (1) associated with at least two first transducers (2.1) connected to a first electronic processor unit (5) via electronic multiplexer means (6) so as to be operated successively in a motor mode and in a detection mode and so as to provide a first detection signal. The vibrating resonator (1) is associated with at least two second transducers (2.2) connected to a second electronic processor unit (4) via two load amplifiers (3.1), two anti-aliasing filters (3.2) and two ADCs (3.3) so as to be operated in the detection mode and to provide a second detection signal. The sensor comprises an electronic hybridization unit (20) for forming a third detection signal from the first and second detection signals.

Description

[0001] The present invention relates to inertial rotation sensors with vibrating resonators. BACKGROUND

[0003] Rotation sensors are devices that measure the component of the angular velocity vector that is collinear with the axis of the sensor, called its "sensitive" axis.

[0004] Known inertial rotation sensors comprise a mechanical resonator, such as a bell or a beam, associated with a transducer arranged to maintain the resonator in vibration and to deliver the measurements to a processing unit arranged to generate information, called "electrical angle", considered to represent the rotation speed undergone by the sensor and projected onto the sensitive axis of the resonator. However, the electrical angle is affected by various imperfections and errors.

[0005] The angular deviation is therefore dependent on the initial conditions and is eliminated by discrete differentiation when calculating the angular velocity.

[0006] By its nature, the velocity deviation and the scale factor of an inertial sensor are functions of the electrical angle in π cycles. The Fourier coefficients that characterize the velocity deviation and the scale factor depend on the individual manufacturing imperfections of the inertial sensor. An individual calibration step performed in the factory is used to compensate for the effect of these imperfections over the working temperature range of the inertial sensor, but this operation is imperfect and, moreover, it has no effect on the variations of the parameters due to ageing.

[0007] The two vibration modes of the resonator are associated by a 2x2 matrix of masses, stiffnesses and dampings, and they exhibit small relative anisotropies compared to the unit, these anisotropies being called "first order" in the sense of a limited development. Nonetheless, these matrices are perfectly symmetric in the mathematical sense of the term, despite the manufacturing imperfections. As a result, the second and zero harmonics of the drift are first and second order, respectively, so that the zero harmonic drift is naturally very small and very stable.

[0008] The errors due to the electronic processing of the signals from the transducer must be minimized and, despite the asymmetry of the transducer, the small value of the zero harmonic drift must be preserved.

[0009] From this, the navigation unit exploits the inertial sensor in such a way as to minimize the effects of the drift harmonics and of the scale factor as much as possible. Nonetheless, the techniques used for this purpose have no effect on the zero harmonic, so that the equipment must preserve the small value of its drift.

[0010] Document EP A 1 541 967 discloses an inertial rotary sensor comprising a vibrating resonator associated with at least two modal orthogonal transducers, each transducer being formed by at least one pair of electrodes and being connected, via multiplexer means, to a common electronic processor unit so that each of these transducers functions in turn:

[0011] • as a motor, under the action of an excitation signal, also called control signal, transmitted successively by the electronic processor unit via a common control branch, so as to maintain the resonator vibrating; and

[0012] • as a detector, the successive measurement signals being sent to the electronic processor unit via a common detection branch, so as to enable the generation of an electrical angle.

[0013] Thus, during the control phase, the processing electronics generate the excitation signal which is applied successively to the transducers when they function as motors, and during the detection phase, the same processing electronics process the measurement signals transmitted by all the transducers when they function as detectors. Thus, when as motors and when as detectors, the anisotropy due to the processing is eliminated and the performance of the sensor is improved since the harmonic drift is minimized.

[0014] In a sensor of the type using a time-sharing sharing operation, the performance depends on the setting time of the electronics, where the time must be as short as possible compared to the duration of the detection and control phases. This means that the electronics must be chosen to have a passband greater than the inverse of the detection duration. This leads to the electronic noise being subjected to a high level of aliasing during the sampling, which greatly reduces the signal-to-noise ratio. Thus, the techniques for maintaining the drift precision require a compromise with a greatly reduced angular noise. This degradation is acceptable for navigation applications, but it is detrimental to driving and prohibits stabilization.

[0015] SUMMARY

[0016] The aim of the present invention is to provide an inertial rotary sensor with a vibrating resonator that at least partially eliminates the above-mentioned drawbacks.

[0017] BRIEF DESCRIPTION OF DRAWINGS

[0018] To achieve this object, the application provides an inertial rotation sensor comprising a vibrating resonator associated with at least two first transducers connected to a first electronic processor unit via electronic multiplexer means so as to be operated successively in a motor mode and in a detection mode and so as to provide at least one first detection signal. The vibrating resonator is associated with at least two second transducers connected to a second electronic processor unit via two load amplifiers and two analog-to-digital converters (ADCs) so as to be continuously operated in a detection mode and to provide at least one second detection signal. The sensor comprises an electronic hybridization unit for forming a third detection signal from the first and second detection signals.

[0019] The first transducers are operated in common time. Thus, in the control mode, the first transducers receive the excitation signals from the same processor unit and, in the detection mode, all the measurement signals emitted by the first transducers are received and processed by the same processor unit: the processing anisotropy is eliminated, thereby enabling navigation to be accurate.

[0020] Conversely, the second transducers are continuously operated, i.e. the second transducers of the inertial sensor are used as detector transducers physically separate from the transducers providing the control (in this example, the transducers are the first transducers in the control mode). The anti-aliasing filter prevents the sampling from reducing the noise density in the analog signal in the vicinity of the resonance frequency, making the angular noise naturally very low. However, the asymmetry of the electronic channel and of the detection transducers degrades the harmonic content of the electrical angle, making the second signal unsuitable for accurate navigation.

[0021] The hybridization unit combines the first and second detection signals so as to provide a third detection signal which can thus benefit from the accuracy of the first detection signal and the low noise of the second detection signal.

[0022] In a particular embodiment, the vibrating resonator is bell-shaped, with a planar annular edge carrying at least one electrode facing an electrode extension fixed to the carrying structure so as to form the electrodes of the first transducers and of the second transducers.

[0023] Alternatively, in this embodiment;

[0024] • the sensor comprises two first transducers which are orthogonal in mode and two second transducers which are orthogonal in mode, each formed by two pairs of electrodes; or

[0025] • the sensor comprises four first transducers forming two groups which are transducers orthogonal in mode and four second transducers forming two groups which are transducers orthogonal in mode, each transducer being formed by two pairs of electrodes.

[0026] FIG. 1

[0027] Other features and advantages of the application will become apparent in the course of the following description of particular, non-limiting embodiments of the application, associated with the appended drawings, in which:

[0028] · FIG. 2 is a block diagram of a sensor of the application;

[0029] · FIG. 1 is a block diagram similar to FIG. 3 illustrating a time-sharing portion of the sensor; and

[0030] · DETAILED DESCRIPTION is a block diagram of a variant sensor of the application.

[0031] FIG. 1

[0032] With reference to FIG. 3 and 2 , in a conventional manner, the inertial rotary sensor of the application comprises a vibrating resonator 1, which in the present example is in the form of a clock. The vibrating resonator 1 is associated with transducers, which in the example are formed by electrodes carried by an electrode carrier structure and facing a ring-shaped electrode carried by a planar ring-shaped edge of the resonator.

[0033] In the example, the transducers comprise first transducers 2.1 (in particular two first transducers referenced 2.11 and 2.12) and second transducers 2.2 (in particular two second transducers referenced 2.21 and 2.22). Each first transducer 2.1 comprises two pairs of electrodes (one pair consisting of an electrode on the carrier structure and the ring-shaped electrode; within each pair, the electrodes face each other), the pairs being diametrically opposite each other (two pairs corresponding to one channel), and each second transducer 2.2 comprises two pairs of electrodes (within each pair, the electrodes face each other), the pairs being diametrically opposite each other (two pairs corresponding to one channel). In the example, the transducers 2.1 and 2.2 are uniformly distributed in angle, and the electrodes fixed to the carrier structure have the same size. The first transducers 2.11 and 2.12 are orthogonal in mode. The second transducers 2.21 and 2.22 are orthogonal in mode.

[0034] The first transducers 2.1 are connected to a first electronic processor unit 6 via a multiplexer stage 5, in order to operate successively in a motor mode and in a detection mode, and in order to provide a first detection signal θ tp . This multiplexer stage 5 is an electronic circuit, and is arranged in a conventional manner to subject the ring-shaped electrode to a direct current (DC) voltage and to act to alternate:

[0035] • demultiplex the control signals provided to it by the processor unit 6 and transmit them successively to the first transducers 2.1 during the control mode in order to transmit them to the motor; and

[0036] • multiplex the measurement signals transmitted to it by each of the first transducers 2.1 when the first transducers 2.1 are in the detection mode and transmit these signals to the electronic processor unit 6.

[0037] The single processor unit 6 is arranged to generate control signals which are transmitted to the first transducers 2.1 in order to place them in the control mode. To this end, in the preferred embodiment, the single processor unit 6 comprises a control branch 7 which comprises a digital-to-analogue converter (DAC) 8 with gain k which converts the digital control signals u into analogue control signals specified by the expression f = ku f . The signals f are transmitted alternately to the first transducers 2.11 and 2.12 via the terminals 16 when the first transducers are in the control mode (corresponding to the control action time). The processor circuit further comprises a detection branch 9 with input terminals 17 which receive the measurement signals alternately from the first transducers 2.11 and 2.12 when the first transducers are in the detection mode (corresponding to the detection action time). The input terminals 17 are connected to the summing input of a load amplifier 14 which converts the current signals i into voltage signals. The detection branch 9 further comprises a corrector member 10 with very high gain, which can be considered as infinite gain, followed by an ADC 11. The first detection signal θ tp is derived from the output signal of the ADC 11 by a processing algorithm known per se. The detection branch 9 is associated with the control branch 7 by means of a switch 12 in order to form a feedback loop which is open during the control action time and closed during the detection action time. The feedback loop further comprises a component 13 for dividing the equivalent impedance of the circuit which is connected to the inverting terminal of the load amplifier 14. It can be seen that, thus, the gain k introduced in the control process and the phase error are eliminated during the detection process, thereby improving the performance of the sensor and minimising the phase error in the quadrature control of the sensor.

[0038] The second transducers 2.2 are connected via a pre-processor stage 3 to the second electronic processor unit 4 in order to operate continuously in the detection mode and provide the second detection signal θ tc .

[0039] Preferably, the pre-processor stage 3 is an electronic circuit comprising, for each of the second transducers 2.2, a load amplifier 3.1 having an input connected to the second transducer 2.2, an anti-aliasing filter 3.2 having an input connected to an output of the load amplifier 3.1, and an ADC 3.3 having an input connected to an output of the anti-aliasing filter 3.2 and an output connected to an input of the electronic processor unit 4. Thus, each second transducer 2.2 forms, together with the load amplifier 3.1, the anti-aliasing filter 3.2 and the ADC 3.3 connected thereto, a detection circuit. The ADC 3.3 is arranged to have a high resolution and a high sampling frequency, such that the noise density due to the analog-to-digital conversion is negligible (as the various different user tolerable noise levels are not all the same, there is no absolute rule, but very good results can be obtained, for example with 20 bits and 1 megahertz (MHz)). The anti-aliasing filter 3.2 is arranged to eliminate frequencies larger than half the sampling frequency, such that the noise density of the analog signal in the vicinity of the resonance frequency is not degraded by the sampling. This ensures that the angular noise obtained is naturally very low.

[0040] The electronic processor unit 4 is itself known and is arranged to generate a second detection signal θ tc from the signals provided by the second transducers 2.2.

[0041] The sensor comprises an electronic hybridization unit 20 for forming a third detection signal θ from the first and second detection signals θ tp and θ tc .

[0042] In this example, the electronic hybridization unit 20 comprises:

[0043] • a low-pass filter 21 having an input connected to the first electronic processor unit 6 so as to receive the first detection signal θ tp and an output connected to a first input of a summing circuit 23 having an output providing the third detection signal θ; and

[0044] • a high-pass filter 22 having an input connected to the second processor unit 4 so as to receive the second detection signal θ tc and an output connected to a second input of the summing circuit 23.

[0045] The low-pass filter 21 and the high-pass filter 22 have complementary transfer functions, i.e. their sum is equal to 1 at all frequencies.

[0046] In operation:

[0047] • the first transducer 2.11 successively passes through an action time cl (corresponding to the control mode of the transducer) and a detection time dl (corresponding to the detection mode of the transducer), wherein the switching from one to the other is controlled by the first electronic processor unit 6;

[0048] • the first transducer 2.12 likewise successively passes through an action time c2 and a detection time d2, wherein the switching from one to the other is controlled by the first electronic processor unit 6;

[0049] • the second transducers 2.21 and 2.22 operate continuously as detectors, and the second electronic processor unit 4 operates continuously to process the measurement signals delivered to it by the second transducers 2.2 via the preprocessor stage 3 in order to generate a second detection signal θ tc ; and

[0050] • the electronic hybrid unit generates a third detection signal θ from the first and second detection signals θ tp and θ tc .

[0051] Thus, the third detection signal θ results from a low-frequency re-setting of the second detection signal θ tc by the first detection signal θ tp .

[0052] The fact that the sensor comprises a single multiplexer stage which, by multiplexing, associates the two first transducers to a single processor unit serves not only to eliminate the anisotropy between the control circuit and the detection circuit of the first transducers depending on whether they are in the control mode or in the detection mode, but also to eliminate the cross-talk between control and detection of each first transducer, so that the performance of the sensor is further improved.

[0053] It should be observed that the present application can be applied to an existing inertial sensor, provided that the number of transducers is sufficient to form one group which operates as a detector on a continuous basis and another group which alternates between acting as a detector and as a motor.

[0054] ​ The sensor in the variant of Fig. 2 differs from the sensor described above in that it has sixteen electrodes fixed to the electrode carrier structure instead of eight electrodes.

[0055] In this example, the transducer comprises four first transducers 2.1 (reference 2.11 to 2.14) and four second transducers 2.2 (reference 2.21 to 2.24). Each first transducer 2.1 comprises two pairs of electrodes (i.e. one electrode on the carrier structure and a ring electrode; and within each pair of electrodes facing each other), which are diametrically opposed to each other (with the two pairs corresponding to one channel). Each second transducer 2.2 comprises two pairs of electrodes (within each pair of electrodes, the electrodes face each other), which are diametrically opposed to each other (with the two pairs corresponding to one channel). In this example, the transducers 2.1 and 2.2 are uniformly distributed in angle and the electrodes fixed to the carrier structure all have the same size. The first transducer groups (2.11, 2.13) and (2.12, 2.14) are orthogonal in mode. The second transducer groups (2.21, 2.23) and (2.22, 2.24) are orthogonal in mode.

[0056] Each of the second transducers 2.21, 2.23, which are physically orthogonal to each other, is connected to a respective amplifier 3.1, one having its output connected to the positive input of a summing circuit 3.15 and the other having its output connected to the negative input of the same summing circuit 3.15. Each of the second transducers 2.22, 2.24, which are physically orthogonal to each other, is connected to a respective amplifier 3.1, one having its output connected to the positive input of a summing circuit 3.15 and the other having its output connected to the negative input of the same summing circuit 3.15. Each summing circuit 3.15 has an output connected to an anti-aliasing filter 3.2, which is connected as above to a respective ADC 3.3, which is connected to the electronic processor unit 4.

[0057] This solution is very advantageous. In particular, this arrangement serves to further reduce the influence of vibrations due to the operating environment. With the solution with eight or sixteen electrodes, the flexural movement of the bell around its support causes a relative variation of the capacitance on diametrically opposed electrodes and these variations are rejected by connecting said electrodes in parallel. Moreover, in the embodiment with sixteen electrodes, the translational movement of the bell with respect to the electrode carrier structure is rejected by differential processing between pairs of electrodes which are physically orthogonal to each other.

[0058] In this sixteen-electrode embodiment, the hybrid algorithm generates θ, taking into account the fact that the electrical angle θ tp and θ tc is offset by 45°.

[0059] Naturally, the present application is not limited to the described embodiments and variants can be applied thereto without departing from the scope of the present application as defined by the claims.

[0060] In particular, the structure of the sensor of the application can differ from the one described.

[0061] The conditioner can have some other shape, and for example, it can comprise vibrating beams parallel to each other, as in the sensor sold by the supplier safran electronics and defense under the "Quapason" trademark, or so-called DELCO angular sensors (for example, with a configuration of eight pairs of electrodes). This sensor can likewise be of the microelectromechanical system (MEMS) type as covered by patent FR-A-2 983 574. Whatever the type of resonator, in the case of sharing the time, it is preferable to use in succession:

[0062] • a single electronic channel for the two axes of vibration mode of the resonator, the two axes being offset by 45° from each other in a bell resonator and by 90° from each other in a quapason type parallel beam resonator and in the resonator covered by patent FR-A-2 983 574; and

[0063] • a respective single transducer group, used as an actuator and then as a detector for each of the two axes.

[0064] The electronic processing and hybridization unit can have a different structure from the one described.

[0065] The electronic processing and hybridization unit they form several parts of a common electronic circuit or several parts of different electronic circuits.

[0066] The principle of hybridization by means of complementary filters as described above is the simplest, but it is naturally possible to envisage hybridizing in other ways, for example such as by Kalman filtering.

[0067] The anti-aliasing filter is optional.

[0068] In a variant, it should be observed that it is advantageous to use a greater number of electrodes in order to benefit from the differential effect suitable for reducing certain errors, for example in order to reject the influence of linear acceleration.

[0069] The transducers can be arranged in an angularly non-uniform distribution.

[0070] These electrodes can have different sizes. In particular, the area of the electrodes of the second transducer can be greater than that of the electrodes of the first transducer.

[0071] The transducers can be capacitive, piezoelectric,...

[0072] In a variant, each first transducer delivers a first detection signal after analog to digital conversion, and each second transducer delivers a second detection signal after analog to digital conversion, and the electronic hybridization unit uses the first and second detection signals to form the third detection signal. The transducers do not necessarily need to be orthogonal in mode.

Claims

1. An inertial rotary sensor comprising a vibrating resonator (1) associated with at least two first transducers (2.1) connected to a first electronic processor unit (6) via electronic multiplexer means (5) so as to operate successively in a motor mode and in a detection mode and to provide at least one first detection signal, the sensor being characterized in that the vibrating resonator (1) is associated with at least two second transducers (2.2) connected to a second electronic processor unit (4) via two load amplifiers (3.1) and two ADCs (3.3) so as to operate continuously in a detection mode and to provide at least one second detection signal, and in that the sensor comprises electronic hybridization means (20) for forming a third detection signal from the first detection signal and the second detection signal.

2. The sensor of claim 1, wherein, The electronic hybridization means (20) comprise: a low-pass filter (21) having an input connected to the first electronic processor unit (6) so as to receive the first detection signal and an output connected to a first input of a summing circuit (23) having an output providing the third detection signal; and a high-pass filter (22) having an input connected to the second electronic processor unit (4) so as to receive the second detection signal and an output connected to a second input of the summing circuit (23).

3. The sensor of claim 2, wherein, The low-pass filter (21) and the high-pass filter (23) have complementary transfer functions.

4. The sensor of any one of claims 1 to 3, wherein, Each first transducer (2.1) comprises two pairs of electrodes facing each other, the two pairs being diametrically opposite each other, and each second transducer (2.2) comprises two pairs of electrodes facing each other, the two pairs being diametrically facing each other.

5. The sensor of any one of claims 1 to 3, wherein, The two second transducers (2.2) are connected to the second electronic processor unit (4) via the two load amplifiers (3.1), via two anti-aliasing filters (3.2), and via the two ADCs (3.3).

6. The sensor of any one of claims 1 to 3, wherein, The vibrating resonator (1) is bell-shaped, having a planar annular edge carrying at least one electrode facing fixed to a carrying structure so as to form an electrode extension of the first transducers (2.1) and of the second transducers (2.2).

7. The sensor of claim 6, wherein, Comprise two first transducers (2.1) that are mode orthogonal and two second transducers (2.2) that are mode orthogonal, each formed by two pairs of electrodes.

8. The sensor of claim 6, wherein, Comprise four first transducers (2.1) forming two groups and four second transducers (2.2) forming two groups, the four first transducers being mode orthogonal transducers, the four second transducers being mode orthogonal transducers, each transducer being formed by two pairs of electrodes.

9. The sensor of any one of claims 1 to 3, wherein, Each first transducer (2.1) delivers a first detection signal after analog-to-digital conversion, and each second transducer (2.2) delivers a second detection signal after analog-to-digital conversion, and the electronic hybridization means (20) use the first detection signal and the second detection signal to form the third detection signal.

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