HK1093097B - Angular speed measuring transducer - Google Patents

Description

Angular velocity measuring sensor

Technical Field

The present invention relates generally to a sensor for measuring angular velocity, formed by a piezoelectric tuning fork rotating at said angular velocity, the tuning fork comprising a base from which an excitation leg and a detection leg extend, and in particular to the arrangement of detection electrodes on the detection leg.

Background

From the prior art, and in particular EP patent 0750177, it is known that a gyrometer formed by a single tuning fork has a base from which extend a first leg on which excitation electrodes are arranged and a second leg on which detection electrodes are arranged.

Fig. 1 shows an example of a tuning fork 1 that can be used in a gyrometer. The tuning fork 1 shown in longitudinal section in fig. 1a mainly comprises a base 2 fixed to two legs 3, 4, the assembly being made of piezoelectric quartz material. As shown in cross-section in fig. 1b, each leg 3, 4 comprises an electrode. The excitation leg 3 comprises a first pair of excitation electrodes 5a, 5b connected to each other, to which an alternating electrical signal is applied at the resonant frequency of the tuning fork, in a main plane corresponding to fig. 1 a; and a second pair of excitation electrodes 6a, 6b connected to each other and to which an alternating current electric signal in phase opposition to the electric signal applied to the electrodes 5a and 5b is applied. The application of these alternating electrical signals excites and thereby causes the legs 3 and 4 of the tuning fork 1 to mechanically vibrate in a first plane, as indicated by arrow 9. The sensing leg 4 comprises a first pair of interconnected sensing electrodes 7a, 7b and a second pair of interconnected sensing electrodes 8a, 8b which convert mechanical vibrations of the sensing leg into electrical signals which are sensed by a sensing circuit connected to said electrodes.

According to the principle of the tuning fork gyrometer, when an excitation signal is applied to the excitation electrodes 5a-5b, 6a-6b, the angular rotation of the tuning fork 1 with respect to its longitudinal axis 10 generates a coriolis force perpendicular to the velocity of the excitation leg and to the rotation axis 10, thus generating a vibration in the detection leg 4 in a plane perpendicular to the plane of the excitation vibration, as indicated by the arrow 11. This mechanical vibration is converted into an electrical signal by the piezoelectric quartz of the tuning fork 1, which is detected by the tuning fork detection electrodes 7a-7b, 8a-8 b.

One major problem observed with this arrangement of detection electrodes is that the electrical path of the field to be detected between the two detection electrodes to which opposite electrical signals are applied is not linear, so that a non-negligible part of the field lines is lost. Such a detection measurement is therefore not optimal.

A theoretically advantageous solution is to arrange two pairs of detection electrodes 7a-7b, 8a-8b as shown in fig. 1 c. However, this solution has a major drawback in that it requires the implementation of complex manufacturing methods that are difficult to control. In practice, the electrodes on the lateral sides of the tuning fork are made by "electrodeposition", which must be carried out over the entire thickness of the lateral sides. It is therefore difficult to divide the electrode deposition into two in order to obtain the two different electrodes 7b, 8b required. Furthermore, such gyrometers are manufactured in batches, i.e. connected to each other. In this way, it is also difficult to divide the electrode deposit made on the outer lateral surface of the tuning fork into two distinct electrodes 7a, 8 b.

Moreover, the solutions described above have the additional drawback that the tuning fork, of course, used on the plate-shaped gyrometer, is preferably as compact as possible, in terms of its dimensions.

Disclosure of Invention

A main object of the present invention is to overcome the above drawbacks by making a sensor for measuring angular velocity in the form of a piezoelectric resonator with a tuning fork having a detection electrode structure that ensures an optimal measurement of the electric field generated in the detection leg, while using a manufacturing method that is easy to implement.

It is therefore within the scope of the invention to arrange the detection electrodes in such a way that on the one hand the manufacturing method thereof is simple and on the other hand the electric field lines detected in the detection legs pass through the detection legs along a substantially straight electrical path between the dissimilar electrodes. For this reason, a protrusion is provided on the side of the tuning fork detection leg so that the detection electrode provided at the top can be easily separated from the detection electrode provided at the bottom of the leg.

Thus, according to a preferred embodiment of the invention, the invention relates to a sensor for measuring angular velocity according to the opening part of the description, characterized in that the detection leg has a cross-shaped cross-section comprising two upper sides and two lower sides, the upper and lower sides being separated by a protruding part protruding with respect to the upper and lower sides, and in that the detection means comprise a first and a second detection electrode arranged with respect to each other, each arranged on one of the upper sides, such that an electric field between the first and the second detection electrode passes the detection leg substantially straight; further comprising third and fourth detection electrodes arranged with respect to each other, each arranged on one of the lower sides such that an electric field between the third and fourth detection electrodes passes the detection leg substantially linearly.

Also, for miniaturization, it is preferable to arrange the mechanical decoupling means at the base of the tuning fork, thus further reducing the size of the latter.

Drawings

Further characteristics and advantages of the invention will become more apparent from reading the detailed description of an embodiment thereof, given by way of non-limiting example only and illustrated by the accompanying drawings.

FIG. 1a, which has been described, is a longitudinal cross-sectional view of a tuning fork for use in a certain type of gyrometer according to the prior art;

FIG. 1b, already described, is a transverse section I-I of the excitation and detection leg of the tuning fork of FIG. 1 a;

FIG. 1c, already described, is a transverse cross-sectional view of the excitation and detection legs of a tuning fork with an optimized arrangement of detection electrodes;

FIG. 2a is a longitudinal cross-sectional view of a tuning fork for a gyrometer according to a first embodiment of the present invention;

FIG. 2b is an enlarged transverse cross-section II-II of the excitation and detection leg of the tuning fork according to FIG. 2 a;

FIG. 2c is an enlarged transverse cross-sectional view of two legs of a tuning fork in accordance with a variation of the first embodiment of the present invention;

FIG. 3a is an enlarged transverse cross-sectional view of the excitation and detection legs of the tuning fork according to the second embodiment of the present invention;

FIG. 3b is an enlarged transverse cross-sectional view of the excitation and detection legs of the tuning fork as modified in accordance with the second embodiment of the present invention.

Detailed Description

According to a first preferred embodiment of the invention, shown in fig. 2a and 2b, the device for measuring angular velocity comprises a sensor formed by a single piezoelectric (conventionally quartz) tuning fork 21 rotating at angular velocity, the tuning fork 21 being formed by a base from which two parallel legs 23, 24 extend, separated by a slot, and each carrying a conductive deposit forming electrodes of opposite polarity, which generate and detect an alternating electric field in the legs, which causes the tuning fork to vibrate due to piezoelectric deformation, which in turn causes an alternating electric field to be formed.

An excitation means 25, 26, referred to as excitation leg 23, is provided on one of the two legs to generate a vibration of the sensor in response to an excitation signal at a predetermined frequency in the first direction, said frequency preferably corresponding to the resonant frequency of the tuning fork in its X-Y plane. Fig. 2b is a cross-sectional view along the axis II-II of fig. 2a, according to the example shown in fig. 2b, the excitation leg 23 preferably having a cross-shaped cross-section comprising two upper sides 31-32 and two lower sides 35-36, which are separated by projections 39-40, said projections 39-40 preferably projecting substantially along the X-axis with respect to the upper and lower sides. According to a first embodiment, the excitation means comprise a first pair of excitation electrodes 25a and 25b arranged on the upper 31-32 and lower 35-36 sides of the excitation legs, respectively, and a second pair of excitation electrodes 26a and 26b or lateral electrodes arranged over the entire thickness of the protruding portions 39 and 40 of the excitation legs, respectively.

The electrodes are arranged to be electrically connected in such a way that their conventional central electrodes 25a and 25b are connected to one pole of the excitation source and the lateral electrodes 26a and 26b are connected to the opposite pole of the excitation source; these connections are mainly achieved by conductive paths deposited on the tuning fork itself. In the example of fig. 2a, the excitation source is shown in the form of an oscillator 43. During operation, the vibration of the resonator can be maintained by bending the excitation leg 23 of the tuning fork, due to the transverse alternating electric field in the plane of the legs 23, 24.

In the other leg of the tuning fork, called the detection leg 24, detection means 27, 28 are provided for generating an electrical detection signal in response to a second vibration of the sensor, having the same predetermined frequency and in a second direction perpendicular to the first direction, due to the first vibration and the rotation about the longitudinal axis 10. The second vibration includes an effective component whose amplitude represents the angular velocity.

The gyrometer including the tuning fork described above further comprises suitable measuring means, shown in the form of a receiver 44, said receiver 44 not being described herein since its structure depends on the purpose for which the angular velocity of the sensor is measured, which measuring means provide a measuring signal representative of the angular velocity by means of an electrical detection signal.

Also according to the example shown in fig. 2b, the sensing leg 23 has a cross-shaped cross-section comprising two upper sides 33-34 and two lower sides 37-38, which are separated by projections 41-42 extending with respect to the upper and lower sides, preferably substantially along the x-axis.

The detection means comprise a first 27a and a second 28a detection electrode, which are arranged on one upper side 33 and the other upper side 34, respectively, with respect to each other, such that the electrical path between the two electrodes 27a and 28a is substantially straight through the detection leg 24. The detection device further comprises a third 27b and a fourth 28b detection electrode, which are arranged with respect to each other on one lower side 37 and the other lower side 38, respectively, such that the electrical path between the two electrodes 27b and 28b is substantially straight through the detection leg 24. Electrodes 27a and 27b are connected to a first pole of detector 44 and electrodes 28a and 28b are connected to a second pole of detector 44, different from the first pole. Thus, the detection of the electric field generated in the detection leg is also optimized while providing a simple electrodeposition method similar to that disclosed in EP patent 0750177.

Also for reasons of miniaturization, it is preferable to arrange the mechanical decoupling 45 between the part 46 for fixing the tuning fork base to the gyrometer and the vibrating legs 23, 24. According to a first variant, these mechanical decoupling means are formed by a notch 45 made in the upper part of the base. According to a second variant, not shown here, these mechanical decoupling means are formed by holes provided in the upper central portion of the base. Combinations of the above variations are also contemplated.

It should be noted that in fig. 2c, 3a and 3b, which will be described below, the oscillator 43 and the detector 44 are not shown again for the sake of simplicity.

Fig. 2c shows a variation of the tuning fork described with respect to fig. 2a and 2 b. This variation differs from the first embodiment in the arrangement of the excitation electrodes on the excitation legs 23.

According to this variant, the excitation means comprise, optionally, a first pair of excitation electrodes 25a and 25b, arranged respectively on the upper and lower sides of the excitation leg, not covering the upper sides 31-32 and the lower sides 35-36, and a second pair of electrodes, or respectively central electrodes 26a and 26b or lateral electrodes, arranged respectively over the entire thickness of the projections 39 and 40 of the excitation leg, and covering at least partially the respective upper and lower sides 31 and 35, 32 and 36.

Fig. 3a shows a cross section of a tuning fork for a gyrometer according to a second embodiment of the present invention. Each excitation leg 23 and detection leg 24 has a substantially cross-shaped cross-section comprising two upper sides 31-32 and 33-34 and two lower sides 35-36 and 37-38, respectively, which are separated by projections 39-40 and 41-42, respectively, preferably projecting substantially along the x-axis relative to the upper and lower sides. Each of the two legs includes a respective top surface 47 and 48 and a respective bottom surface 49 and 50, which are preferably substantially in the X, Y plane.

In the example shown in fig. 3a, the excitation leg 23 comprises two slots 51-52 etched in its top surface 47 and two slots 53-54 etched in its bottom surface 49. However, it is contemplated that only one groove may alternatively be provided on each of the top and bottom surfaces.

The excitation means comprise a first excitation electrode 25a arranged on the top surface 47 so as to laterally cover the grooves 51-52 and a second excitation electrode 25b arranged on the bottom surface 49 so as to laterally cover the grooves 53-54. The excitation means further comprise third 26a and fourth 26b excitation electrodes, or lateral electrodes, connected to a potential opposite to the potential to which the first electrodes 25a and 25b are connected, and arranged over the entire thickness of the respective projections 39 and 40 of the excitation legs, and at least partially covering the upper 31 and 32 and lower 35 and 36 lateral sides.

In the same manner, sensing leg 24 includes two slots 55-56 etched in its top surface 48 and two slots 57-58 etched in its bottom surface 50. Each slot 55-58 has a side. However, it is contemplated that only one slot may alternatively be provided on the top and bottom surfaces for the excitation leg. It should also be noted that the provision of slots on both faces provides a symmetrical leg cross-section which prevents deformation of the leg on its out-of-plane side. The provision of the grooves promotes the generation of a uniform electric field along the electrical axis X of the crystal.

Referring again to FIG. 3a, the sensing device includes a first pair of sensing electrodes 27a-28a disposed relative to each other, electrode 28a disposed on upper side 33, and the other electrode 27a disposed on one side of well 55 such that the electric field between the two electrodes 27a and 28a is substantially linear through leg 24, and a third pair of sensing electrodes 27c-28c disposed relative to each other, electrode 27c disposed on upper side 34, and the other electrode 28c disposed on one side of well 56 such that the electric field between the two electrodes 27c and 28c is substantially linear through leg 24. In a symmetrical manner, the detection device comprises a second pair of detection electrodes 27b-28b arranged with respect to each other, electrode 28b being arranged on lower side 38, the other electrode 27b being arranged on one side of slot 58 so that the electric field between the two electrodes 27b and 28b passes substantially straight through leg 24, and a fourth pair of detection electrodes 27d-28d arranged with respect to each other, electrode 27d being arranged on lower side 37, the other electrode 28d being arranged on one side of slot 57 so that the electric field between the two electrodes 27d and 28d passes substantially straight through detection leg 24.

According to the second embodiment, the depth of the longitudinal grooves 55-58 eroded on each of the top and bottom surfaces of the excitation and detection legs is between 20% and 45%, preferably around 30%, of the thickness of the leg.

Providing electrodes in slots etched in the thickness of the legs improves the piezoelectric coupling. This increase results in a reduction of the tuning fork equivalent resistance at the same dimensions, thus reducing the power consumption of the oscillator associated therewith, this arrangement allowing a reduction of the resonator dimensions, with an equal quality factor.

According to a variation of the second embodiment, the excitation leg and the detection leg have only one slot on each of the top and bottom surfaces, as shown in fig. 3 b. In this case, the excitation electrodes provided on the top and bottom surfaces of the excitation leg laterally cover the respective grooves. With regard to the sensing devices, they include a first pair of sensing electrodes 27a-28a disposed relative to one another, with electrode 28a disposed on upper side 33 and the other electrode 27a disposed on one side of slot 59 such that the electric field between the two electrodes 27a and 28a passes substantially linearly through sensing leg 24, and a third pair of sensing electrodes 27c-28c disposed relative to one another, with electrode 27c disposed on upper side 34 and the other electrode 28c disposed on the other side of slot 59 such that the electric field between the two electrodes 27c and 28c passes substantially linearly through sensing leg 24. In a symmetrical manner, the detection means comprise a second pair of detection electrodes 27b-28b arranged with respect to each other, electrode 28b being arranged on lower side 38, the other electrode 27b being arranged on one side of slot 60 so that the electric field between the two electrodes 27b and 28b passes substantially linearly through leg 24, and a fourth pair of detection electrodes 27d-28d arranged with respect to each other, electrode 27d being arranged on lower side 37, the other electrode 28d being arranged on the other side of slot 60 so that the electric field between the two electrodes 27d and 28d passes substantially linearly through detection leg 24.

It should be noted that preferably, as shown in fig. 2a, 2b and 3a, 3b, the piezoelectric tuning fork is quartz, with major top and bottom surfaces substantially perpendicular to the optical axis (z) of the quartz, and the legs extending substantially along the mechanical axis (y) of the quartz.

It is clear that a person skilled in the art may make various variations and modifications to the various embodiments of the invention described in the present description, particularly it should be noted that the detection leg and the excitation leg may be interchanged, thus using the excitation leg as the detection leg and vice versa, without departing from the invention as defined by the appended claims; mechanical decoupling means may be used for each of the embodiments previously proposed; a so-called cross-type (cross) electrode tuning fork solution is possible, where the excitation electrode pair and the detection electrode pair are reversed between the two legs.

Claims (8)

1. A sensor for measuring angular velocity, formed by:

a single piezoelectric tuning fork (21) rotating at said angular velocity,

the tuning fork comprises a first vibrating leg (23) and a second vibrating leg (24) extending from a base,

means (25a, 25b, 26a, 26b) for exciting a first vibration of the tuning fork, arranged on one of the two legs, called excitation leg (23),

means (27a, 27b, 28a, 28b) for detecting a second vibration of the tuning fork, said second vibration being generated in response to said first vibration and to a rotation of the tuning fork, said detection means being arranged on the other of said two legs, called detection leg (24),

characterized in that said detection leg (24) has a cross-shaped cross-section comprising two upper sides (33, 34) and two lower sides (37, 38), said upper and lower sides being separated by projections (41, 42) projecting with respect to said upper and lower sides, and

the detection means comprise a first detection electrode (27a) and a second detection electrode (28a) arranged with respect to each other, each of which is arranged on one of the upper sides (33, 34) such that an electric field between the first and second detection electrodes passes substantially linearly through the detection leg; further comprising a third detection electrode (27b) and a fourth detection electrode (28b) arranged relative to each other, each of which is arranged on one of said lower sides (37, 38) such that an electric field between said third and fourth detection electrodes passes substantially linearly through said detection leg.

2. Sensor for measuring angular velocity according to claim 1, characterized in that the excitation leg (23) has a cross-shaped cross-section comprising two upper sides (31, 32) and two lower sides (35, 36), the upper sides (31, 32) and the lower sides (35, 36) of the excitation leg (23) being separated by a first projection (39) and a second projection (40) projecting with respect to the upper sides (31, 32) and the lower sides (35, 36) of the excitation leg (23), and in that

Said excitation means comprising a first pair of excitation electrodes (25a, 25b) arranged respectively at the upper and lower part of said excitation leg, covering the upper (31, 32) and lower (35, 36) sides of said excitation leg (23), respectively; further comprising a second pair of excitation electrodes (26a, 26b), each electrode of said second pair of excitation electrodes (26a, 26b) being arranged on the thickness of one said protruding portion (39) or the other said protruding portion (40) of said excitation leg.

3. Sensor for measuring angular velocity according to claim 1, characterized in that the excitation leg (23) has a cross-shaped cross-section comprising two upper sides (31, 32) and two lower sides (35, 36), the upper sides (31, 32) and the lower sides (35, 36) of the excitation leg (23) being separated by a first projection (39) and a second projection (40) projecting with respect to the upper sides (31, 32) and the lower sides (35, 36) of the excitation leg (23), and in that

The excitation means comprises a first pair of excitation electrodes (25a, 25b) arranged respectively at the upper and lower parts of the excitation leg, not covering the upper (31, 32) and lower (35, 36) sides of the excitation leg (23); further comprising a second pair of excitation electrodes (26a, 26b), each electrode of said second pair of excitation electrodes (26a, 26b) being arranged on the thickness of one (39) or the other (40) of said excitation legs and at least partially covering the upper (31) and lower (35) sides of said excitation legs (23) arranged on either side of said first projection (39), the upper (32) and lower (36) sides of said excitation legs (23) arranged on either side of said second projection (40), respectively.

4. Sensor for measuring angular velocity according to any of claims 1 to 3, characterized in that the cruciform cross-section of the detection leg has a top face (48) connecting the two upper side faces (33, 34) of the detection leg (24) and a bottom face (50) connecting the two lower side faces (37, 38) of the detection leg (24),

each of said top and bottom surfaces having at least one groove (55, 58; 59, 60), said groove having side surfaces,

at least one electrode (27a) of a first pair of detection electrodes comprising said first detection electrode (27a) and a second detection electrode (28a) is arranged on one of said side faces of said at least one groove (55; 59) on said top face such that an electric field between said first detection electrode (27a) and said second detection electrode (28a) passes substantially linearly through said detection leg, and

at least one electrode (27b) of a second pair of detection electrodes comprising the third detection electrode (27b) and a fourth detection electrode (28b) is arranged on one side of the at least one groove (58; 60) on the bottom surface such that an electric field between the third detection electrode (27b) and the fourth detection electrode (28b) passes substantially linearly through the detection leg (24).

5. Sensor for measuring angular velocity according to claim 4, characterized in that each of said top (48) and bottom (50) faces comprises a single groove (59, 60),

the detection device further comprises a third pair of detection electrodes (27c, 28c) arranged with respect to each other, one electrode (28c) of the third pair of detection electrodes (27c, 28c) being arranged on the other side of the groove (59) of the top surface, the other electrode (27c) of the third pair of detection electrodes (27c, 28c) being arranged on the upper side (34) of the detection leg (24) such that an electric field between the two electrodes of the third pair of detection electrodes (27c, 28c) passes substantially linearly through the detection leg (24), and

the detection device further comprises a fourth pair of detection electrodes (27d, 28d) arranged with respect to each other, one electrode (28d) of the fourth pair of detection electrodes (27d, 28d) being arranged on the other said side of the slot (60), the other electrode (27d) of the fourth pair of detection electrodes (27d, 28d) being arranged on the lower side (38) of the detection leg (24) such that an electric field between the two electrodes of the fourth pair of detection electrodes (27 d; 28d) passes substantially straight through the detection leg.

6. Sensor for measuring angular velocity according to claim 4, characterized in that each of said top (48) and bottom (50) faces comprises two grooves (55-56, 57-58),

the detection device further comprises a third pair of detection electrodes (27c, 28c) arranged with respect to each other, one electrode (28c) of the third pair of detection electrodes being arranged on one side of the other slot (56) of the top surface, the other electrode (27c) of the third pair of detection electrodes being arranged on an upper side (34) of the detection leg (24) such that an electric field between the two electrodes of the third pair of detection electrodes (27c-28c) passes substantially linearly through the detection leg, and

the detection device further comprises a fourth pair of detection electrodes (27d, 28d) arranged relative to each other, one electrode (28d) of the fourth pair of detection electrodes (27d, 28d) being arranged on one of the side faces of the other one (57) of the two slots, the other electrode (27d) of the fourth pair of detection electrodes (27d, 28d) being arranged on the lower side face (37) of the detection leg such that an electric field between the two electrodes of the fourth pair of detection electrodes (27d, 28d) passes the detection leg substantially straight.

7. Sensor for measuring angular velocity according to claim 1 or 2, characterized in that the piezoelectric tuning fork is quartz, with its top (48) and bottom (50) surfaces essentially perpendicular to the optical axis (z) of the quartz, and the legs essentially extending along the mechanical axis (y) of the quartz.

8. Sensor for measuring angular velocity according to claim 1 or 2, characterized in that the base is provided with mechanical decoupling means (45) between a part (46) for fixing the base and the legs (23, 24) of the tuning fork.