Vibration gyrometer with a planar structure

Abstract

The inertial angular position sensor comprises at least three equivalent resonators (R1 to R3) arranged symmetrically around the sensitive axis (AA) of the sensor. As a result, a gyrometer constituted by said sensor has an integrating function. Said sensor further comprises a connecting element (Ec) connecting the vibrating part of each resonator to the vibrating parts of all other resonators of the sensor. The preferred configuration of the inertial angular position sensor makes it possible to obtain an integrating gyrometer with high sensitivity and low manufacturing costs.

Description

Detailed Description of the Invention

[0001] [Technical Field] The present invention relates to an inertial angular position sensor and a gyroscope including the sensor. The present invention provides a plurality of models for a gyroscope having a planar structure. The planar structure can be manufactured by an integral (integrated) etching process, and each of the planar structures provides the function of an integrating gyroscope. The present invention is applicable to both piezoelectric materials such as quartz crystals and other crystal materials (e.g., silicon) common in the field of microsystems.

[0002] [Prior Art] As is known, it is possible to form a gyroscope from at least one vibrating part having at least two individual vibration modes. In this case, these two modes can be coupled to each other by the rotation applied to at least one vibrating part. Therefore, the gyroscope includes, in addition to the (at least one) vibrating part, (i) means for exciting one of the two vibration modes (referred to as the pilot mode), and (ii) means for detecting the amplitude of the vibration in the other mode (referred to as the sensing mode).

[0003] In an article called an integrating gyroscope, the value directly measured is not the rotational speed but the value corresponding to the rotation angle by which the gyro has rotated with respect to the Galilean reference system. This operating principle is known as the "inertia of the body's vibration" and was demonstrated using a pendulum by Léon Foucault in 1851. This relates to the resulting manifestation of the inertial force when the inertial force clarified by Gustave Coriolis acts on one or more resonators that do not have any preferred axis of vibration. Directly measuring the result of time-integrating the angular velocity can be very beneficial in highly dynamic applications and when information about angular deviation is essential. For example, this is true particularly in applications of inertial navigation.

[0004] As theorized in Lord Brian's 1892 paper, "On a revolving cylinder or bell," Proceedings of the Cambridge Philosophical Society, Volume VII, October 28, 1889 - May 30, 1892, the well-known integral gyrometer described above uses a hemispherical resonator or bell. In this resonator configuration, rotation causes partial tuning of the resonator vibrations, resulting from the partial transfer of vibrational energy between the two degenerate modes in the resonator.

[0005] As is known, two vibration modes are said to be degenerate if (i) they correspond to separate categories of geometric distortion (deformation) of the resonator, but (ii) they have the same vibration frequency value. Throughout this specification, vibration modes of a resonator or inertial angular position sensor are simply described as one of its natural vibration modes. That is, in the absence of external interference, vibrations in the process in this mode continue without mixing with other natural vibration modes of the resonator or sensor. In the case of a gyrometer, it is the Coriolis force that causes coupling between the two natural modes. As a result, vibrations excited according to one of the two natural modes are partially or completely transmitted to the other natural mode. The intensity of this transmission of vibrational energy yields a measurement of rotational speed. Or, in the case of an integrating gyrometer, the intensity yields a measurement of rotational angle.

[0006] Another example of an integrating gyrometer is based on a beam designed (intended) to flexurally vibrate. This beam is made of an isotropic material and has a cross-section such that its bending inertia is equivalent in at least two different bending directions. This is especially true if the beam's cross-section is circular, square, or isosceles triangle, and more generally, if the beam does not have a preferred axis of bending vibration, as opposed to a beam with a rectangular cross-section. The reader will understand that (i) any asymmetry in the beam or the embedded object within the support may impair the desired effect, and (ii) in order to obtain the vibration inertia, the vibrating part must be considered isolated from the outside world. This means that the vibration is independent of the mounting of the vibrating part. Furthermore, the material of the vibrating part may need to have symmetry suitable for the vibration under consideration.

[0007] In the case of resonators in the form of microsystems, a planar structure is required. This allows the resonator to be easily realized by an integrated manufacturing process based on a wafer of a material selected for forming one or more resonators in a gyrometer. Conventionally, this material is single-crystal or polycrystalline silicon, or quartz crystal.

[0008] In silicon-based resonators, the motion of a mass is typically controlled by electrostatic force. This resulting motion is then typically detected by capacitance measurements performed on at least one capacitor formed between the moving and stationary parts.

[0009] In the case of resonators made of piezoelectric materials, the useful excitation of vibrations due to the piezoelectric effect, and the useful signals detected, no longer originate from motion, but from mechanical stress or strain. Consequently, resonator structures in which stress and strain are distributed across the extended region of the resonator are more suitable for piezoelectric materials than structures that take the form of a non-deformable inertial mass associated with a spring, where stress and strain are present only in the portion of the material acting as a spring.

[0010] The paper "The theory of a piezoelectric disc gyroscope", JS Burdess et al., IEEE Transactions on Aerospace And Electronic Systems, 1986, Volume: AES-22, issue 4, proposes an integral gyroscope having a planar structure and made of piezoelectric material. The resonator considered in this paper has a disk shape. The two degenerate modes of vibration of this resonator are selected by the design of the excitation and detection electrodes. The vibrating electronic circuit is made possible to follow the natural (intrinsic) precession of the vibration when the resonator is subjected to rotation on an axis orthogonal to the disk. The main drawback of this gyroscope is the resonator's great sensitivity to mounting conditions. That is, the mounting area located at the center of the disk must be sufficiently large to allow for effective mounting of the resonator. However, this mounting area greatly changes the frequency and damping of the two useful modes of vibration. In most cases, the mounting area causes losses in the degeneracy of the two modes, making it difficult, or even impossible, to function as an integral gyroscope. For example, improvements have been proposed for FR2,723,635 by using higher-order modes, but sufficient isolation of the resonator from the environment has not been achieved.

[0011] As described in US7,040,163, disk shapes corresponding to the resonator were also used in conjunction with silicon materials by proposing an aperture disk that allows for the insertion of means for electrostatic excitation and means for detecting the capacitive nature of vibration modes. However, as is the case with disks made of piezoelectric materials, sufficient degeneracy of vibration modes cannot be achieved with central mounting. Furthermore, central mounting requires the use of complex and expensive balancing and / or electronic compensation techniques.

[0012] As described in the paper "Flat is not dead: current and future performance of Si-MEMS Quad Mass Gyro (QMG) system", AA Trusov et al., DOI: 10.1109 / PLANS.2014.6851383, other vibration structures implement (i) rigid bodies and (ii) means of connecting the mass bodies, with non-deformable mass bodies connected to them. The structure described in that paper consists of four mass bodies connected to each other in pairs by a system of levers to force opposite-phase motion. However, these levers are complex to manufacture and require a high level of manufacturing precision to obtain symmetry between vibration modes in the plane of the structure. Therefore, this structure requires the introduction of an auxiliary system to balance useful modes, particularly by adding electrostatic rigid bodies.

[0013] Reference CN106,441,261A describes a micromechanical gyroscope with four oscillating mass bodies connected to an inner ring and an outer ring. These connections to the inner ring are made by levers. The entire gyroscope is invariant to a 90° rotation.

[0014] [Technical issues] Based on this situation, an object of the present invention is to provide a novel inertial angular position sensor for an integrating gyrometer. As described above, the gyrometer improves upon at least some of the shortcomings of conventional sensors.

[0015] A secondary objective of the present invention is to provide a sensor that reduces external vibration energy loss in order to increase the quality factor value and to more easily obtain two degenerate modes.

[0016] Another secondary objective of the present invention is to reduce symmetry defects that may affect the shape of a sensor when the sensor is manufactured by a wet chemical etching process. The wet chemical etching process is a low-cost manufacturing process due to the difference in etching rates that exist between different crystal orientations of the material used to form the sensor.

[0017] [Overview of the prefecture] To achieve at least one of these or other objectives, a first aspect of the present invention proposes a novel inertial angular position sensor. The sensor comprises at least three equivalent resonators arranged symmetrically around an axis referred to as a sensing axis. The resonators are invariant to rotations of 2π / n around this sensing axis, where n is the number of resonators in the sensor. The n resonators are connected to one another such that the sensor has at least two degenerate modes of vibration. This makes it possible to characterize the rotation of the sensor around the sensing axis.

[0018] According to the first configuration of the sensor of the present invention, each resonator includes a portion of a wafer having two flat and parallel opposing surfaces. The wafer portion dedicated to each resonator is designed to vibrate when the sensor is in use and is referred to as the vibrating portion of the resonator. Furthermore, the wafer is common to the n resonators of the sensor.

[0019] According to the second configuration of the sensor of the present invention, each vibrating part is designed to vibrate in a bending manner when the sensor is in use.

[0020] Finally, according to a third configuration of the sensor of the present invention, the sensor further comprises a connecting element. The connecting element connects the vibrating portion of each resonator to all the other vibrating portions of the n resonators of the sensor. The connecting element is also invariant to a rotation of 2π / n around the sensing axis. The vibrating portions of the n resonators are angularly distributed around the connecting element.

[0021] The sensor of the present invention can be manufactured industrially at low cost using a wafer-based integrated manufacturing process designed to form each of the vibrating parts of the n resonators.

[0022] In addition, the inertial angular position sensor of the present invention is suitable for being part of an integrating gyrometer because it has two degenerate modes of vibration. In these two modes of vibration, vibrational energy is readily transferred from one mode to the other by the rotation of the sensor around the sensing axis relative to the Galilean reference frame. More precisely, the number of individual resonators forming the sensor (3 or more) allows the presence of a pair of degenerate modes of vibration to be combined with the possibility of rotation around the sensing axis that transfers energy between these degenerate modes. As described above, the two degenerate modes have a common vibration frequency value. However, the sensor may have multiple vibration frequency values, each associated with one of the two degenerate modes of vibration.

[0023] Finally, since the connection element of the sensor of the present invention is invariant to a rotation of 2π / n around the sensing axis of the sensor, it is possible to maintain the degeneracy between the two modes in the vibration of the set of resonators while ensuring good efficiency when transmitting vibration energy between the two degenerate modes of vibration with respect to the rotation around the sensing axis to be measured. Thus, the sensor provides high detection and measurement sensitivity to the gyrometer in which the sensor is incorporated.

[0024] Preferably, the number of resonators n in the sensor is 8 or less.

[0025] Preferably, each vibrating part may be designed to bend and vibrate parallel to the surface of the wafer when the sensor is in use.

[0026] Preferably, the connecting element may be composed of a pattern formed integrally (integrated) with each vibrating part of the resonator of the sensor in the wafer.

[0027] According to the fourth configuration of the present invention, the vibrating part of each resonator is connected to the support part of the sensor located outside the vibrating part and the connecting element by an intermediate segment (portion) of the wafer called a foot. The foot is integrated with the vibrating part and forms a connecting part between the vibrating part and the support part. And for each resonator, it is as follows.

[0028] The vibrating part of this resonator has: (i) a first plane of symmetry (referred to as the central plane) that is parallel to both surfaces of the wafer and equidistant from these two surfaces, and (ii) a second plane of symmetry (referred to as the plane of symmetry perpendicular to the wafer) that is perpendicular to the central plane and passes longitudinally through the connecting part formed by the foot located between the support part and the vibrating part. (i) The common part (intersection) of the central plane and (ii) the plane of symmetry perpendicular to the wafer forms the central axis of the vibrating part. The vibrating part has two extending parts. Each of the two extending parts is designed to bend and vibrate. These two extending parts extend symmetrically from the foot to each side of the plane of symmetry perpendicular to the wafer. Each extending part is provided with a longitudinal slot. The slot passes through the vibrating part perpendicular to the central plane, starting from the plane of symmetry perpendicular to the wafer and heading towards the distal end of this extending part but not reaching the distal end. As a result, each extending part has a meandering shape. The slots in each of the two extended portions are symmetric with respect to a plane of symmetry perpendicular to the wafer, and intersect in this plane of symmetry perpendicular to the wafer. As a result, the vibrating portion comprises two primary segments and two secondary segments. The two primary segments each connect their feet to one distal end of the extended portion. The two secondary segments are interconnected by their respective proximal ends in the plane of symmetry perpendicular to the wafer. Each of the two secondary segments extends to one distal end of the extended portion, where it connects to one of the segments of the primary segment.

[0029] According to the above configuration of each vibrating portion of the sensor's resonator, for both degenerate modes of sensor vibration that enable characterization of rotation around the sensing axis, this vibrating portion is parallel to the central plane and involves only motion symmetric with respect to a plane of symmetry perpendicular to the wafer. Furthermore, both primary segments have an instantaneous velocity component parallel to the central axis at each point in time during vibration. The direction of this instantaneous velocity component is opposite to that of the instantaneous velocity component of the secondary segment. The instantaneous velocity component of the secondary segment is also parallel to the central axis. These opposite velocity directions allow some of the momentum components associated with them to compensate for each other at least partially for each resonator. Therefore, the motion transmitted to the foot of the resonator by the vibrating portion is reduced. As a result, the resonator has low vibrational energy loss. Therefore, its quality factor can be high. For this reason, the quality factor of the sensor effective for each of the two degenerate vibration modes is also high.

[0030] Beneficially, for each resonator, each degenerate mode of sensor vibration, parallel to the central plane and involving only motion symmetric with respect to a plane of symmetry orthogonal to the wafer, may have a mass distribution in the vibrating portion such that it does not cause any movement of the foot parallel to the central axis of the resonator under consideration. In other words, compensation for the momentum component of each vibrating portion parallel to the central axis of the resonator under consideration can be precise (exact) or nearly precise. In this case, the vibration energy loss through the foot of the resonator is zero or nearly zero. Therefore, the quality factor of the sensor for the two degenerate modes of vibration can be very high. In addition, by preventing the aforementioned movement of the foot, the sensor can be made less sensitive to symmetry defects, which may occur during mounting to an external base and may eliminate degeneracy between vibration modes.

[0031] Each extension of each resonator may include an extension at its distal end, parallel to the central plane, to the longitudinal edge (end) outside the primary and secondary segments of the extension. This extension provides an additional degree of freedom, which allows for compensation of the momentum component parallel to the central axis within each vibrating portion. Thus, the design of resonators that do not transmit motion through the foot is facilitated.

[0032] Beneficially, in a preferred embodiment of the present invention, the connecting element may be connected to the vibrating portion of each resonator parallel to the central axis of the resonator and on the side of the vibrating portion opposite to the foot portion, at the interconnected proximal end of the secondary segment. The above configuration of the sensor increases the transmission of vibrational energy generated by rotation to be measured in the two degenerate modes of vibration. Thus, the sensitivity of the sensor is further increased.

[0033] Beneficially, the wafer material may be a single crystal, may belong to the trigonal system, and may be piezoelectric. In this case, for each resonator of the preferred embodiments of the present invention described above, the central axis of the vibrating portion may be parallel to the axis Xc of the material. Both the primary and secondary segments of this vibrating portion may be parallel to the axis Yc of the material. In other words, one of the extensions of each vibrating portion may be parallel to the crystal axis Yc+, and the other may be parallel to the crystal axis Yc-. Thus, their extensions form an angle equal to 60° between them. Therefore, each sensor resonator may be symmetrical, since it is manufactured directly using a wet chemical etching process for etching the sensor pattern into the wafer. In particular, wafers may be made (i) from α-quartz crystals (α-SiO2), (ii) from any other trigonal class 32 crystal such as gallium orthophosphate (GaPO4), germanium oxide (GeO2), gallium arsenate (GaAsO4), or (iii) from crystals of the LGX family, i.e., langasite (LGS, i.e., La3Ga5SiO2). 14 ), LGT (i.e., La3Ga5,5TaO,5O 14 ), or langanite (LGN, i.e., La3Ga5,5NbO,5O 14 ) may be created by.

[0034] Alternatively, the extensions of both vibration portions may form an angle equal to 90° or 180° between them.

[0035] Generally speaking, the sensor in this invention is - Excitation means adapted to generate bending strain in the vibrating portion of n resonators according to the first of several degenerate modes of sensor vibration, -A detection means adapted to measure the vibration amplitude of the sensor according to a different vibration degeneracy mode than the first vibration degeneracy mode, It also possesses.

[0036] Finally, a second aspect of the present invention relates to a gyrometer comprising a sensor according to the first aspect of the present invention. The function of the gyrometer is to use the coupling produced by the Coriolis force between two degenerate modes of vibration. Its type is an integrating gyrometer.

[0037] [Brief description of the drawing] The configuration and advantages of the present invention will become clearer from the following detailed description of several non-limiting and exemplary embodiments by referring to the accompanying drawings. The drawings include the following: Figure 1a is a plan view of the first inertial angular position sensor according to the present invention; Figure 1b corresponds to Figure 1a and shows the first degenerate mode of vibration in the first inertial angular position sensor; Figure 1c corresponds to Figure 1b and shows the second degenerate mode of vibration in the first inertial angular position sensor; Figure 2a corresponds to Figure 1a and relates to the second inertial angular position sensor according to the present invention; Figure 2b corresponds to Figure 1b and relates to the second inertial angular position sensor; Figure 2c corresponds to Figure 1c and relates to the second inertial angular position sensor; Figure 3a corresponds to Figure 1a and relates to the third inertial angular position sensor according to the present invention; Figure 3b corresponds to Figure 1b and relates to the third inertial angular position sensor; Figure 3c corresponds to Figure 1c and relates to the third inertial angular position sensor; Figure 4a corresponds to Figure 1a and relates to the fourth inertial angular position sensor according to the present invention; Figure 4b corresponds to Figure 1b and relates to the fourth inertial angular position sensor; Figure 4c corresponds to Figure 1c and relates to the fourth inertial angular position sensor; Figure 5a is a plan view showing a first resonator model usable in a preferred embodiment of the present invention; Figure 5b corresponds to Figure 5a and shows the strain in the vibration mode of the first resonator model, along with the associated momentum; Figure 5c corresponds to Figure 5a and relates to a second resonator model usable in other preferred embodiments of the present invention; Figure 5d corresponds to Figure 5b and relates to the second resonator model; Figure 6a corresponds to Figure 1a and relates to a fifth inertial angular position sensor according to the present invention, using the first resonator model shown in Figures 5a to 5b; Figure 6b corresponds to Figure 1b and relates to the fifth inertial angular position sensor; Figure 6c corresponds to Figure 1c and relates to the fifth inertial angular position sensor; Figure 7a corresponds to Figure 1a and relates to a sixth inertial angular position sensor according to the present invention, using the second resonator model shown in Figures 5c to 5d; Figure 7b corresponds to Figure 1b and relates to the sixth inertial angular position sensor; Figure 7c corresponds to Figure 1c and relates to the sixth inertial angular position sensor; Figure 8a corresponds to Figure 1a and relates to the seventh inertial angular position sensor according to the present invention; Figure 8b corresponds to Figure 1b and relates to the seventh inertial angular position sensor; Figure 8c corresponds to Figure 1c and relates to the seventh inertial angular position sensor; Figure 9 shows a feasible electrode configuration suitable for piezoelectric coupling that can be used to excite and detect bending vibrations of a beam in the case of a beam material (e.g., α-quartz) that is piezoelectric and belongs to the trigonal system and symmetry class 32.

[0038] [Detailed description of the invention] For clarity, the dimensions of each element shown in these figures do not correspond to actual dimensions or actual dimensional ratios. In particular, the distortions of all illustrated resonators are exaggerated to a degree for better visibility. Furthermore, the same reference numerals shown in different figures indicate the same element or measurement, or an element or measurement having the same function.

[0039] All figures except Figure 9 show inertial angular position sensors or resonators etched into the interior of a solid material wafer having two flat, parallel surfaces. These figures are illustrated in a plane parallel to the two surfaces of the wafer, located between these two surfaces, and equidistant from these surfaces. This plane is the plane of symmetry for each sensor or resonator and is referred to as the central plane. For small sensors created by a single etching process, the thickness of the wafer used (measured perpendicular to the aforementioned surfaces) can range from a few micrometers to a few millimeters.

[0040] Figures 1a-1c, 2a-2c, 3a-3c, and 4a-4c do not correspond to the inventions described in each claim. Furthermore, the explanatory parts provided with respect to these figures are intended to facilitate understanding of the present invention and its advantages.

[0041] Figure 1a shows a first inertial angular position sensor 101 according to the present invention, having four resonators (i.e., n=4). The sensor includes a support portion in the form of a square peripheral frame. This support portion is indicated by reference numeral Pf and is also referred to as the fixed portion. This fixed portion Pf is designed to fix the sensor 101 to a base (not shown) and to establish electrical contact between electrodes (not shown) supported by the resonators and an electronic excitation / detection circuit (not shown). Four beams P are arranged inside the frame of the fixed portion Pf, parallel to and spaced apart from the four sides of the frame. Each beam P is connected to the fixed portion Pf by two feet Pd located at the corners of the fixed portion Pf at its two opposing ends. Thus, each foot Pd is shared by two adjacent beams P. Each beam P can then bend and vibrate between its two ends parallel to the central plane. Therefore, each beam P constitutes a separate resonator. The four resonators are individually indicated by reference numerals R1, R2, R3, and R4. Thus, each beam P constitutes a vibrating portion of each resonator. Sensor 101 further comprises a cross-shaped connecting element indicated as Ec. The connecting element Ec, like the beam P and the foot Pd, is etched into the wafer. The ends of the arms of the connecting element Ec are connected one-to-one to the centers of each beam P. Thus, the entire sensor 101, comprising the fixed part Pf, the foot Pd, the beam P, and the connecting element Ec, is orthogonal to the central plane and invariant to a rotation of π / 2 about an axis passing through the center of the sensor. The sensor has two degenerate modes corresponding to the vibration displacement at the center point of the connecting element Ec. As shown in Figure 1b, in the first mode, the vibration displacement is parallel to the X-axis. Also, as shown in Figure 1c, in the second mode, the vibration displacement is parallel to the Y-axis. Due to symmetry, these two modes are degenerate, each having the same vibration frequency value. Furthermore, the Coriolis force applied to the connecting element Ec, generated by the rotation of the sensor around axis AA, which is orthogonal to the wafer and passes through the center of the sensor, results in the coupling of these two degenerate modes.Thus, the rotation of the sensor 101 results in the transfer of vibrational energy from one mode to the other. Therefore, this first inertial angular position sensor 101 is suitable for creating an integral gyrometer having axis AA as the sensing axis.

[0042] Figure 2a shows a second inertial angular position sensor 102 according to the present invention, having three resonators (i.e., n=3). The design of this second sensor is similar to that of the first sensor in Figure 1a, except that the square shape of the frame of the fixed part Pf is replaced with an equilateral triangular shape. Thus, the second sensor comprises (i) three individual resonators R1 to R3, and (ii) a connecting element Ec having three arms. Each of the resonators R1 to R3 is formed by two opposing ends of a beam P connected to the fixed part Pf. Each of the three arms is spaced 120° apart from its adjacent arm. Each arm of the connecting element Ec is still connected to the center of one of the three beams P. This second sensor 102 still has a first mode and a second mode as two degenerate modes of vibration. As shown in Figure 2b, in the first mode, the center point of the connecting element Ec undergoes vibrational motion parallel to the X-axis. Furthermore, as shown in Figure 2c, in the second mode, the center point of the connecting element Ec undergoes oscillating motion parallel to the Y-axis. Therefore, this second inertial angular position sensor 102 is also suitable for creating an integrating gyrometer.

[0043] However, in the two sensors shown in Figures 1a-1c and 2a-2c, the momentum involved in each of the degenerate modes of vibration is not compensated. Therefore, the fixed part Pf is moved by a motion opposite to the movement of the resonator set and connecting element Ec. This motion is transmitted to the fixed part Pf via the foot Pd. As a result, the sensor becomes very sensitive to the mounting conditions of the fixed part Pf to the external base. In particular, the loss of symmetry between the X and Y axes caused by these mounting conditions results in the degeneracy of the two eigenmodes of vibration of the sensor being hindered. In this case, the gyroscope no longer functions as an integrator. However, the conditions for mounting the fixed part Pf to the external base are generally not well controlled (especially when this mounting is done with adhesive). In addition, the motion transmitted to the fixed part Pf causes a loss of vibrational energy in multiple modes of vibration. This generates resonant overpotential, reducing the sensitivity of the gyroscope. The improvements of the present invention described below overcome this drawback.

[0044] This improvement allows each resonator in the sensor to be balanced individually. As a result, each resonator is dynamically isolated from the fixed part Pf. Therefore, the vibration of each resonator does not cause motion in the (multiple) feet to which it is connected. Consequently, there is no loss of vibrational energy through the feet. Therefore, the degenerate mode of vibration in the sensor is less sensitive to symmetry defects that occur when the fixed part Pf is mounted on an external base. As a result, a gyrometer incorporating the sensor can have a high-performance integration function. In other words, this improvement in the present invention involves using an intrinsically balanced resonator model in addition to an n-th order axially symmetric arrangement of the inertial angular position sensor.

[0045] As mentioned above, resonators separated from a fixed part are known from the prior art. Examples of the prior art include (i) the double-ended tuning fork described in particular in US4,215,570, and (ii) the simple double-ended blade having inertial masses at both ends described in FR8,418,587.

[0046] In other words, this improvement of the present invention involves using an intrinsically balanced resonator model in an n-th order axially symmetric arrangement of inertial angular position sensors.

[0047] The third inertial angular position sensor 103 in Figure 3a still uses the fourth-order (n=4) axisymmetric of the sensor in Figure 1a, except that this sensor uses a resonator model based on tuning forks at both ends. Thus, each of the resonators R1 to R4 is composed of two beams P1 and P2 that are parallel to each other and extend between the two feet Pd to which the resonators are connected. Preferably, each of the resonators R1 to R4 has an intermediate region ZI between the beams P1 and P2 and each foot Pd. Two beams are embedded within this intermediate region ZI. The intermediate region ZI eliminates the residual forces that would otherwise be transmitted to the feet Pd by the beams P1 and P2. Furthermore, to balance the inertial contributions made by the connection element Ec of the resonator to the beam P1, an additional inertial mass MI is rigidly connected to the beam P2 of each resonator. Preferably, each of the additional inertial mass MI may be composed of a wafer segment. The center of the wafer segment is connected to the center of beam P2. As a result, the stiffness of the wafer segment is not changed, or the symmetry in the resonator is not compromised. Figures 3b and 3c then show two degenerate modes of vibration effective for the sensor, involving the movement of the connecting element Ec parallel to the X-axis or Y-axis, respectively. For each of these modes of vibration degeneracy, the two beams P1 and P2 vibrate in opposite phases, moving away from each other, and then moving toward each other due to their respective bends parallel to the central plane. Therefore, no resulting force is transmitted to each foot Pd of the sensor 103. Consequently, the fixed part Pf of the sensor 103 remains stationary during each of the two degenerate modes of vibration. As a result, the gyroscope can have a high-performance integration function.

[0048] The fourth inertial angular position sensor 104 in Figure 4a still uses the fourth-order (n=4) axial symmetry of the sensor in Figure 1a. However, in this example, the sensor forms each of the resonators R1 to R4 using the resonator model described in FR8,418,587. Thus, each resonator comprises two inertial masses MI1 and MI2. Each of these inertial masses is connected to a fixed part Pf by its respective foot Pd, which acts as a hinge. In addition, the inertial masses MI1 and MI2 are connected to each other by a flexible segment S. When each of the resonators R1 to R4 vibrates, the two inertial masses MI1 and MI2 rotate in opposite directions while moving parallel to the wafer plane toward the same side. Meanwhile, the central part of the flexible segment S moves toward the opposite side. Each arm of the connecting element Ec is connected to the center of one of the flexible segments S of the resonators R1 to R4. Therefore, by adopting dimensions corresponding to the inertial mass bodies MI1 and MI2 that take into account the mass of the connecting element Ec, and, in some cases, by adding an additional inertial mass body to the center of the connecting element Ec, each resonator R1 to R4 appears to be individually balanced within the sensor 104. Figures 4b and 4c show two degenerate modes of vibration of the sensor 104, accompanied by the movement of the connecting element Ec parallel to the X-axis or Y-axis, respectively. A gyrometer incorporating this fourth inertial angular position sensor 104 can have a high-performance integration function.

[0049] However, the two sensor configurations shown in Figures 3a and 4a are bulky and therefore not very suitable for applications requiring a high level of miniaturization. Figures 5a and 5c show two novel resonator models that, according to improvements of the present invention, are still balanced and can be used in inertial angular position sensors. Furthermore, these two novel resonator models can be fabricated in smaller dimensions compared to the resonator models shown in Figures 3a and 4a.

[0050] Unlike conventional resonators, the resonators in Figures 5a and 5c are connected to the fixed part Pf by only one foot Pd. Furthermore, each resonator is individually composed of a vibrating part having two extending parts (denoted P1 and P2, respectively) that extend longitudinally along their respective axes A1 and A2. In the resonator of Figure 5a, axes A1 and A2 form an angle α equal to 60° between them. In the resonator of Figure 5c, the angle α between axes A1 and A2 is equal to 180°. The two extending parts P1 and P2 extend symmetrically from the foot Pd to each side of a central axis Xm that coincides with the longitudinal direction of the foot Pd. This central axis Xm corresponds to the intersection of (i) the central plane already described and (ii) another plane of symmetry perpendicular to the wafer plane. The two extending parts P1 and P2 correspond to mirror symmetry with respect to this plane of symmetry. For the remainder of this specification, by analogy with the tuning fork resonator described in US3,683,213, the two extensions P1 and P2 are also referred to as beams P1 and P2. According to the original characteristics of the resonator in Figures 5a and 5c, longitudinal slots indicated by reference numerals FL1 and FL2, respectively, are provided in each beam P1 and P2. These two longitudinal slots FL1 and FL2 intersect at the central axis Xm of the resonator. Thus, for subscript i equal to 1 or 2, each beam Pi is composed of two blades Liext and Liint. For the rest of this specification, blade L1ext (or L2ext) is referred to as the primary segment of extension P1 (or P2), and blade L1int (or L2int) is referred to as the secondary segment of extension P1 (or P2). Therefore, the two blades L1ext and L2ext are connected to the foot Pd and extend toward the distal ends of beams P1 and P2, respectively. At these distal ends, the two blades L1ext and L2ext are connected one-to-one with the two blades L1int and L2int. Thus, each beam or extension P1, P2 has a meandering shape between its central axis Xm and its distal end.In addition, blades L1int and L2int are interconnected at the central axis Xm by their respective proximal ends. Furthermore, the two longitudinal slots FL1 and FL2 of beams P1 and P2 intersect at the central axis Xm. Thus, the joints at the proximal ends of the two blades L1int and L2int are separated from blades L1ext and L2ext, as well as from the foot Pd.

[0051] In the resonator shown in Figure 5a, as shown in Figure 5b, when the resonator vibrates, if the distal ends of the extensions P1 and P2 move symmetrically away from the central axis Xm in opposite directions, then blades L1ext and L2ext have momentums MV1 and MV2, respectively. MV1 and MV2 are oriented obliquely and symmetrically, pointing toward the same side as the foot Pd. Therefore, the common joint between blades L1int and L2int has momentum MV12. Momentum MV12 is parallel to the central axis Xm and points away from the foot Pd. As a result, blades L1int and L2int each have momentum oriented obliquely and symmetrically toward the side of the resonator opposite to the foot Pd. Therefore, the mass distribution in the vibrating portion between all blades L1ext and L2ext and L1int and L2int can be such that the movement of the foot Pd due to these momentums is 0 or nearly 0. By eliminating the movement of the foot Pd in ​​this way, the transfer of vibration energy from the vibrating part to the support Pf can be zero or very low. Therefore, the quality factor of the resonator can be high. The optimized distribution of mass between the four blades of the vibrating part is still symmetric with respect to the central axis. This distribution can be obtained by assigning a common thickness eext to two blades L1ext and L2ext. eext is different from the thickness (denoted as eint) of the two blades L1int and L2int. By applying this optimization, the resonator is balanced. The blade thicknesses eext and eint are measured parallel to the wafer plane. The resonator dimension values ​​that provide the above balancing may be determined according to several methods, in particular by using finite element calculations.

[0052] As also shown in Figure 5a, according to two modifications to the resonator that can be used independently of each other, the vibrating portion of the resonator can be captured by (i) two inertial masses MI1 and MI2 corresponding to the first modification, and (ii) a stem Pc corresponding to the second modification. Preferably, the two inertial masses MI1 and MI2 are located at the distal ends of two beams P1 and P2 and are equivalent. The two inertial masses can each be formed by extending the corresponding beams P1 and P2 at their distal ends. The stem Pc can be formed by an additional blade. The additional blade extends from the joint at the proximal ends of blades L1int and L2int, parallel to the central axis Xm, and in a direction away from the foot Pd, so as to coincide with the central axis Xm. Advantageously, the stem Pc is also symmetric with respect to the central axis Xm. By adding two inertial masses MI1 and MI2, and / or the stem Pc, to the vibrating portion of the resonator, the resonator can be balanced using additional degrees of freedom. Thus, balancing can be further facilitated. Figure 5b shows the motion of inertial masses MI1 and MI2 at the same time point during resonator vibration, along with the motion of the stem Pc. The two inertial masses MI1 and MI2 have momentum components MV1 and MV2 along the central axis Xm that are in the opposite direction (opposite) to the momentum component MV12 of the stem Pc. These momentum components of inertial masses MI1 and MI2, as well as the stem Pc, combine with the momentum components of the four blades L1ext, L2ext, L1int, and L2int to result in the motion of the foot Pd, which is 0 or nearly (substantially) 0.

[0053] In the resonator shown in Figure 5c, as shown in Figure 5d, during resonator vibration, the two inertial masses MI1 and MI2 move in phase and parallel to the central axis Xm. The junction between blades L1int and L2int also moves parallel to the central axis Xm, but in opposite phase to the inertial masses MI1 and MI2. This results in at least partial compensation of the momentum involved. As a result, the movement of the foot Pd can be reduced or eliminated by determining appropriate dimensions for the resonator. The inertial masses MI1 and MI2 are necessary to achieve accurate balancing of the resonator. The stem Pc, on the other hand, is optional. However, the stem provides an additional degree of freedom regarding the dimensions that result in balancing of the resonator.

[0054] The fifth inertial angular position sensor 105 in Figure 6a is obtained from the second sensor in Figure 2a by using the resonator model in Figure 5a instead of the single-beam resonator model in which each of the resonators R1 to R3 is held by its two ends. Each foot Pd of the three resonators R1 to R3 is connected to a fixed part Pf at one of the corners of a triangular frame formed by the fixed part Pf. Figures 6b and 6c then show two degenerate modes of vibration effective for the fifth sensor, with the movement of the connecting element Ec parallel to either the X or Y axis.

[0055] The sixth inertial angular position sensor 106 in Figure 7a is also obtained from the second sensor in Figure 2a. However, in this example, for each of the resonators R1 to R3, the resonator model in Figure 5c is used instead of the single-beam resonator model held by two ends. The foot Pd of each of the three resonators R1 to R3 is connected to the fixed part Pf at the center of one of the sides of the frame formed by the fixed part Pf. Figures 7b and 7c then show two degenerate modes of vibration effective for the sixth sensor, with the movement of the connecting element Ec parallel to either the X or Y axis.

[0056] Finally, the seventh inertial angular position sensor 107 in Figure 8a is obtained from the first sensor in Figure 1a. However, in this example, for each of the resonators R1 to R4, the resonator model of Figure 5a, in which the angle α is equal to 90°, is used instead of the single-beam resonator model held by two ends. The foot Pd of each of the four resonators R1 to R4 is connected to the fixed part Pf at one of the corners of the square frame formed by the fixed part Pf. Figures 8b and 8c then show two degenerate modes of vibration effective for the seventh sensor, with the movement of the connecting element Ec parallel to either the X or Y axis.

[0057] Since these fifth, sixth, and seventh inertial angular position sensors are fabricated using individually balanced resonators, a high-performance integrating gyrometer with high or very high quality factor values ​​can be obtained, particularly in pilot mode and sensing mode. The gyroscope thus obtained can be extremely sensitive.

[0058] Beneficially, all of the above-mentioned angular inertia position sensors may be (i) made from a single crystal wafer of α-quartz (α-SiO2), (ii) made from any other single crystal of trigonal class 32 such as gallium orthophosphate (GaPO4), germanium oxide (GeO2), gallium arsenate (GaAsO4), or (iii) made from crystals of the LGX family, i.e., langasite (LGS, i.e., La3Ga5SiO2). 14 ), LGT (i.e., La3Ga5,5TaO,5O 14 ), or langanite (LGN, i.e., La3Ga5,5NbO,5O 14) may be created by these materials, which are piezoelectric. In this case, if the resonator of the model in Figure 5a or the model in Figure 5c is used, the orientation of the beams P1 and P2 of each resonator of the sensor (i.e., their longitudinal axes A1 and A2) is advantageously selected to be parallel to the crystal axes Yc, Yc+, and Yc-. The wafer plane is parallel to the crystal plane Xc-Yc. By orienting the sensor pattern with respect to the crystal of the wafer as described above, it is possible to excite pilot modes according to their respective bending vibrations in the crystal plane Xc-Yc and to benefit from optimal piezoelectric coupling for detecting sensing modes. In fact, the piezoelectric tensor of a trigonal crystal class provides optimal coupling according to the strain Syy along the axis of each beam, accompanied by an electric field Exx. This makes it possible to (i) excite the bending vibration of the pilot modes by the direct piezoelectric effect using electrodes positioned along the blades to generate an electric field Exx, and (ii) detect the strain Syy using the charge generated by the indirect piezoelectric effect at these same electrodes. For this reason, several different electrode configurations are known. As shown in Figure 9, according to the first of these configurations, three electrode segments are arranged on each side of each blade that coincides with one of the wafer faces. The electrodes in this first configuration are easily manufactured by a conductive material deposition process. According to another possible configuration, two electrode segments are arranged on each side of each blade that is perpendicular to the wafer face. As described, for example, in US4,524,619, this other configuration is more effective but more difficult to implement. Also, by orienting the sensor pattern with respect to the wafer crystal, the wet chemical etching rate can benefit from the crystal axis Z. That is, the wet chemical etching rate along the crystal axis Z becomes faster. This axis Z is perpendicular to the wafer face used. In this case, the sensor can be manufactured at low cost by a wet chemical etching process, particularly a process using a mixture of ammonium fluoride (NH4F) and hydrofluoric acid (HF).Furthermore, each resonator according to Figure 5a or Figure 5c, which is fabricated in a wafer of a trigonal single-crystal material of symmetry class 32 and has the orientation described above with respect to the crystal axis, can be directly obtained at the end of the wet chemical etching step without symmetry defects. In this way, each resonator is directly balanced, so the multiple resonators in the inertial angular position sensors of Figures 6a and 7a are strictly equivalent.

[0059] As described above, the ability to fabricate sensor patterns using only the wet chemical etching process is particularly beneficial due to the low cost achieved by this integrated manufacturing process tailored to microdevices. In addition, the wet chemical etching process preserves the inherent quality factors of the crystal. In fact, chemical etching is based on localized reactions that cause dissolution of the crystal atom by atom. This fact means that chemical etching does not alter the crystal lattice of the remaining wafer material forming the sensor. This is not true in the case of etching based on localized polishing, such as ultrasonic machining, which uses fine polishing particles excited by ultrasound generated between a probe (sonotrode) and the surface to be etched, or ion collisions, which use the kinetic energy of ions. These last two techniques alter the crystal lattice at the etching edge over characteristic distances ranging from tens of nanometers to several micrometers for the highest energy etching. Therefore, the inherent quality factors of the resonator can be reduced more and more when significant miniaturization of the sensor is desired.

[0060] It is understood that the present invention is not limited to trigonal piezoelectric materials of symmetry class 32. The principle of equivalent resonators, which are separated from the mounting portion, arranged in an axially symmetric configuration, and connected to one another by axially symmetric connecting elements, may be combined with the use of other materials, particularly silicon crystals. Considering the cubic crystal structure of single-crystal silicon, arrangements based on four resonators, such as those shown in Figures 1a, 3a, 4a, and 8a, are preferred. In this case, the excitation of the pilot mode can be achieved by applying an electrostatic force. The amplitude in the sensing mode can be determined by measuring the capacitance between the fixed portion of the sensor and the movable portion of the sensor. [Brief explanation of the drawing]

[0061] [Figure 1a] This is a plan view of the first inertial angular position sensor according to the present invention. [Figure 1b] This corresponds to Figure 1a and shows the first degenerate mode of vibration in the first inertial angular position sensor. [Figure 1c] This corresponds to Figure 1b and shows the second degenerate mode of vibration in the first inertial angular position sensor. [Figure 2a] This corresponds to Figure 1a and relates to a second inertial angular position sensor according to the present invention. [Figure 2b] This corresponds to Figure 1b and relates to the second inertial angular position sensor. [Figure 2c] This corresponds to Figure 1c and relates to the second inertial angular position sensor. [Figure 3a] This corresponds to Figure 1a and relates to a third inertial angular position sensor according to the present invention. [Figure 3b] This corresponds to Figure 1b and relates to the third inertial angular position sensor. [Figure 3c] This corresponds to Figure 1c and relates to the third inertial angular position sensor. [Figure 4a] This corresponds to Figure 1a and relates to a fourth inertial angular position sensor according to the present invention. [Figure 4b] This corresponds to Figure 1b and relates to the fourth inertial angular position sensor. [Figure 4c] This corresponds to Figure 1c and relates to the fourth inertial angular position sensor. [Figure 5a] This is a plan view showing a first resonator model usable in a preferred embodiment of the present invention. [Figure 5b] This corresponds to Figure 5a, which shows the strain in the vibration mode of the first resonator model, along with the associated momentum. [Figure 5c] This relates to a second resonator model, which corresponds to Figure 5a and can be used in other preferred embodiments of the present invention. [Figure 5d] This corresponds to Figure 5b and relates to the second resonator model. [Figure 6a] This invention relates to a fifth inertial angular position sensor that corresponds to Figure 1a and uses the first resonator model shown in Figures 5a to 5b. [Figure 6b] This corresponds to Figure 1b and relates to the fifth inertial angular position sensor. [Figure 6c] This corresponds to Figure 1c and relates to the fifth inertial angular position sensor. [Figure 7a] This invention relates to a sixth inertial angular position sensor that corresponds to Figure 1a and uses the second resonator model shown in Figures 5c to 5d. [Figure 7b] This corresponds to Figure 1b and relates to the sixth inertial angular position sensor. [Figure 7c] This corresponds to Figure 1c and relates to the sixth inertial angular position sensor. [Figure 8a] This corresponds to Figure 1a and relates to the seventh inertial angular position sensor according to the present invention. [Figure 8b] This corresponds to Figure 1b and relates to the seventh inertial angular position sensor. [Figure 8c] This corresponds to Figure 1c and relates to the seventh inertial angular position sensor. [Figure 9] This document presents a feasible electrode configuration suitable for piezoelectric coupling, which can be used to excite and detect bending vibrations of beams in beam materials (e.g., α-quartz) that are piezoelectric and belong to the trigonal crystal system and symmetry class 32.

Claims

1. Inertial angular position sensors (101-107), It includes at least three equivalent resonators (R1-R3; R1-R4) that are symmetrically arranged around an axis called the sensing axis (A-A) and are invariant with respect to a rotation of 2π / n around the sensing axis, n is the number of resonators in the sensor, The n resonators (R1-R3; R1-R4) are connected to each other such that the sensor has at least two degenerate modes of vibration, making it possible to characterize the rotation of the sensor around the sensing axis (A-A). Each resonator (R1-R3; R1-R4) includes a portion of the wafer having two flat and parallel opposing surfaces. Each dedicated wafer portion for the resonator is referred to as the vibrating portion of the resonator, and is designed to undergo bending vibration when the sensor is in use. The wafer is common to the n resonators (R1 to R3; R1 to R4) of the sensor. The sensor further includes a connecting element (Ec) that connects the vibrating portion of each resonator (R1 to R3; R1 to R4) to all the other vibrating portions of the n resonators of the sensor. The aforementioned connecting element is also invariant with respect to a rotation of 2π / n around the sensing axis (A-A), The vibrating portions of the n resonators are arranged angularly around the connecting element, The vibrating portion of each resonator (R1-R3; R1-R4) is connected to the sensor support portion (Pf), which is located outside the vibrating portion and the connecting element (Ec), by an intermediate segment of the wafer called a foot portion (Pd) dedicated to the resonator. The foot portion is integrated with the vibrating portion and forms a foot portion (Pd) between the support portion and the vibrating portion. For each resonator (R1-R3; R1-R4), The vibrating portion of the resonator is A first symmetrical plane that is parallel to both sides of the wafer and equidistant from both sides, It has a second plane of symmetry that is perpendicular to the first plane of symmetry and passes through the foot portion (Pd) located between the support portion and the vibrating portion in the longitudinal direction, The common portion of the first plane of symmetry and the second plane of symmetry forms the central axis (Xm) of the vibrating portion. The vibrating portion includes two extended portions (P1, P2) each designed to undergo bending vibration. The two aforementioned extending portions extend symmetrically from the foot portion (Pd) to both sides of the second plane of symmetry, Each extended portion (P1, P2) is provided with longitudinal slots (FL1, FL2) that extend from the second plane of symmetry toward the distal end of the extended portion, but do not reach the distal end, and pass through the vibrating portion perpendicular to the first plane of symmetry. Each extended portion has a bent shape. Each of the aforementioned slots (FL1, FL2) of both extensions (P1, P2) is symmetric with respect to the second plane of symmetry and intersects in the second plane of symmetry. The vibrating portion includes two primary segments (L1ext, L2ext) and two secondary segments (L1int, L2int), Each of the two primary segments connects the foot portion (Pd) to one distal end of the extension portion, The two secondary segments are interconnected in the second plane of symmetry by their respective proximal ends. Each of the two secondary segments extends toward the distal end of one of the extending portion, and at the distal end is connected to one of the primary segments. For both degenerate modes in the sensor that enable the characterization of rotation around the sensing axis (A-A), The vibrating portion of each resonator is parallel to the first plane of symmetry and is accompanied only by motion symmetrical with respect to the second plane of symmetry. Both primary segments (L1ext, L2ext) have an instantaneous velocity component parallel to the central axis (Xm) at each point in time during the oscillation. A sensor in which the direction of the instantaneous velocity component is opposite to the direction of the instantaneous velocity component of the secondary segment (L1int, L2int) which is parallel to the central axis (Xm).

2. The sensor according to claim 1, wherein the connecting element (Ec) is formed by a pattern formed on the wafer and is integrated with the vibrating portion of each resonator (R1 to R3; R1 to R4).

3. For each resonator (R1-R3; R1-R4), The sensor according to claim 1 or 2, wherein each degenerate mode of vibration of the sensor, which is parallel to the first plane of symmetry and involves only motion symmetric with respect to the second plane of symmetry, has a mass distribution such that the vibrating portion does not cause any movement of the foot portion (Pd) parallel to the central axis (Xm) of the sensor.

4. The sensor according to any one of claims 1 to 3, wherein each extended portion (P1, P2) of each resonator (R1 to R3) has an extension at the distal end of the extended portion parallel to the first plane of symmetry, with respect to the longitudinal edges outside the primary segment (L1ext, L2ext) and the secondary segment (L1int, L2int) of the extended portion.

5. The sensor according to any one of claims 1 to 4, wherein the connecting element (Ec) is connected to the vibrating portion of each resonator (R1 to R3; R1 to R4) at the interconnected proximal ends of the secondary segments (L1int, L2int), parallel to the central axis (Xm) of the resonator, and on the side of the vibrating portion opposite to the foot portion (Pd) of the resonator.

6. The wafer material is a single crystal, belongs to the trigonal crystal system, and is piezoelectric. For each resonator (R1-R3; R1-R4), The central axis (Xm) of the vibrating portion is parallel to the axis Xc of the material. The sensor according to any one of claims 1 to 5, wherein both of the primary segments (L1ext, L2ext) and both of the secondary segments (L1int, L2int) of the vibrating portion are parallel to the axis Yc of the material.

7. The sensor according to any one of claims 1 to 6, wherein the extended portions (P1, P2) of both vibrating parts of each resonator (R1 to R3; R1 to R4) form an angle (α) equal to 60°, 90°, or 180° between the extended portions.

8. An excitation means for generating bending strain in the vibrating portions of the n resonators (R1 to R3; R1 to R4) according to the first degenerate mode among the degenerate modes of vibration, The sensor according to any one of claims 1 to 7, further comprising detection means for measuring the vibration amplitude of the sensor according to another degenerate mode of vibration, which is different from the first degenerate mode of vibration.

9. A gyrometer equipped with an inertial angular position sensor, The sensor is a gyrometer according to any one of claims 1 to 8.

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