Vibrating gyroscope and corresponding manufacturing process

A vibrating gyroscope having a base, and a resonator. The resonator includes a body of generally cylindrical shape terminating in a distal face to the side opposite the base. The face includes at least one through hole, a plurality of piezoelectric elements placed in contact with the resonator, vibration control and processing modules arranged at least in part on the base, and at least one electrical connection passing through the body of the resonator via the hole, and electrically connecting the modules of the base and the plurality of piezoelectric elements for controlling and measuring the vibration of the resonator.

GENERAL TECHNICAL FIELD

The invention relates to a vibrating gyroscope and a process to make such a gyroscope.

STATE OF THE ART

Vibrating gyroscopes are currently used in numerous fields, especially because of their solidity, their reduced electrical consumption, and their rapid execution.

These gyroscopes comprise a resonator which can take various forms, such as a bell or a tuning fork.

The invention relates more particularly to resonators comprising a body of generally cylindrical shape.

The axis z is conventionally designated as the axis of the cylinder, the axes x, y being arranged in the plane orthogonal to the axis z.

It is known that such a resonator in vibration deforms itself preferably elliptically, with four vibration antinodes regularly arranged over the circumference of the cylinder in the plane x, y. A first vibration mode53,57of the resonator is illustrated inFIG. 1, at two given instants, relative to its rest state54. The resonator passes from ellipse53to ellipse57at the end of a semi-period, but this is still the same vibration mode.

Any rotation of the gyroscope about the axis z generates Coriolis forces which have a tendency to cause offset in rotation of vibration antinodes about the circumference of the cylinder. Piezoelectric detection elements, placed at the level of the vibration antinodes, measure a signal which variation determines the angular rotation speed and/or the angle of rotation about the axis z.

By way of illustration, it is evident inFIG. 1that rotation of the resonator causes secondary vibration in elliptical mode52,58whereof the principal axes x1, y1are located at 45° from the axes x, y. Vibration passes from ellipse52to ellipse58at the end of a semi-period.

The signal measured by the piezoelectric detection elements at the level of these axes especially determines the angular rotation speed.

In general, gyroscopes comprise four piezoelectric detection elements for maintaining the vibration of said resonator, and four other piezoelectric elements for measuring the vibration signal of the resonator. These eight elements are most often arranged uniformly about the resonator (four on axes x, y and four on axes x1, y1).

However, the gyroscopes with cylindrical resonator known to date have the disadvantage of being less compact and difficult to manufacture. Also, they are highly sensitive to the vibratory environment.

Therefore a solution improving devices of the prior art should be proposed.

PRESENTATION OF THE INVENTION

For this purpose, the invention proposes a vibrating gyroscope characterised in that it comprises a base, a resonator, comprising a body of generally cylindrical shape terminating in a distal face, to the side opposite the base, said face comprising at least one through hole, a plurality of piezoelectric elements placed in contact with the resonator, modules for vibration control and processing, arranged at least in part in the base, and at least one electrical connection passing through the body of the resonator via said hole, and electrically connecting said modules of the base and the plurality of piezoelectric elements for controlling and measuring the vibration of the resonator.

The invention is advantageously completed by the following characteristics, taken singly or in any of their technically possible combinations:the face comprises a plurality of through holes arranged over its circumference, and said gyroscope also comprises a plurality of electrical connections passing through at least one sub-assembly of said holes for electrical connection of the base modules with the plurality of piezoelectric elements;the holes are arranged substantially uniformly over the circumference of the face, and the piezoelectric elements are arranged between said holes;the gyroscope comprises an interconnection circuit connecting the plurality of electrical connection, and being connected to the piezoelectric elements;the gyroscope comprises a linking foot between the resonator and the base, said foot being arranged at the level of the extension of a central hole of the face of the resonator;the control and processing modules of the base and the piezoelectric elements are connected by at least one electrical connection passing through the linking foot;part of the piezoelectric elements is capable of detecting vibrations of the resonator and the other part of the piezoelectric elements is capable of exciting the resonator in vibration;each piezoelectric element at the same time comprises a sub-element capable of detecting vibrations of the resonator and a sub-element capable of exciting the resonator in vibration;the resonator is capable of vibrating according to a first vibration mode, comprising antinodes distributed on two axes, and a second vibration mode comprising antinodes distributed on two other axes, the face of the resonator on each axis of the first and of the second vibration modes comprising two piezoelectric assemblies, each piezoelectric assembly at the same time comprising at least one piezoelectric sub-element capable of exciting the resonator in vibration and at least one piezoelectric sub-element capable of detecting vibrations of the resonator.

The invention likewise proposes a making process of a vibrating gyroscope, comprising steps consisting of providing a base, forming a resonator comprising a body of generally cylindrical form terminating in a distal face, to the side opposite the base, said face comprising at least one through hole, disposing a plurality of piezoelectric elements in contact with the resonator, mechanically assembling the resonator on the base, placing vibration control and processing modules in the base, and electrically connecting said base modules and the plurality of piezoelectric elements via at least one electrical connection passing through the body of the resonator via said hole for controlling and measuring vibration of the resonator.

The invention has numerous advantages.

An advantage of the invention is to propose a more compact vibrating gyroscope.

An advantage of the invention is to propose a vibrating gyroscope having a lower angular derive.

Another advantage of the invention is to propose a gyroscope easier to manufacture.

Yet another advantage of the invention is to propose a gyroscope having lower production costs.

Finally, another advantage of the invention is to propose a gyroscope less sensitive to the vibratory environment.

DETAILED DESCRIPTION

FIG. 2shows an embodiment of a vibrating gyroscope1according to the invention.

The gyroscope1comprises a base2, which acts as plinth. The gyroscope1also comprises a certain number of vibration control and processing modules18, described later, and placed at least in part in the base2. In general, these modules18are arranged on an electronic control card integrated into the lower part of the base2, and covered by a protective cap.

The gyroscope1also comprises a resonator3. This resonator3comprises a body4of generally cylindrical shape terminating in a distal face5, to the side opposite the base2.

The resonator3is generally a metallic piece.

The face5is particular in that it comprises at least one through hole13. In the embodiment ofFIG. 2the face5comprises a plurality of through holes13.

The gyroscope1also comprises a plurality of piezoelectric elements10, placed in contact with the resonator3. Advantageously, these piezoelectric elements10are disposed on the face5of the resonator3, turned to the exterior of the resonator3. These piezoelectric elements10are designed to measure the vibration of the resonator3and maintain it. These are generally piezoelectric electrodes.

For example, it is known to use lead zirconate titanate as piezoelectric material.

The gyroscope1has at least one electrical connection15, passing through the interior of the body of the resonator3via said hole13, and electrically connecting said modules18of the base2to the plurality of piezoelectric elements10, for controlling and measuring the vibration of the resonator3. This connection15could be relayed by an interconnection card20, acting as an interface between the connection15and the piezoelectric elements10.

As is it evident, this configuration creates a highly compact gyroscope, since the electrical connections between the control and measuring modules18and the piezoelectric elements10are made via the interior of the body of the resonator3, via at least one dedicated hole13of the face5of the resonator3opposite the base2.

Advantageously, the face5comprises a plurality of through holes13arranged on its circumference, as illustrated inFIGS. 2 and 4.

In this case, the gyroscope1also comprises a plurality of electrical connections15passing through at least one sub-assembly of said holes13, for the electrical connection of the modules18of the base2and the plurality of piezoelectric elements10.

The rest of the holes can be used for the entry of mechanical links, for example rods22serving to mechanically link the interconnection card20with the base2.

Advantageously, the holes13are arranged substantially uniformly over the circumference of the face5, that is, with regular or quasi-regular angular offset.

In this case, it is advantageous to place the piezoelectric elements10between said holes.

Advantageously, the holes13are shaped as a disc made in the face5of the resonator described earlier.

Advantageously, the resonator comprises a central hole arranged at the centre of the face5and prolonged by a linking foot21between the resonator3and the base2. This linking foot can have various functions and especially act as mechanical link between the resonator and the base, and/or allow passage for electrical connections between the modules of the base and the piezoelectric elements. The foot is arranged inside the body the resonator.

Advantageously, the base2comprises a recess of shape complementary to the foot21, and capable of receiving the linking foot21to mechanically join the resonator and the base.

In general, the gyroscope1comprises an interconnection card20connecting the plurality of electrical connection15and being connected to the piezoelectric elements10.

This interconnection card20is used for transmission of information or commands sent by the control and processing modules18to the piezoelectric elements, or vice versa.

In general, part of the piezoelectric elements10is capable of exciting the resonator in vibration, and the other part of the piezoelectric elements10is capable of detecting vibrations of the resonator.

Eight piezoelectric elements could be used for example, arranged uniformly on the face5of the resonator3, with four of said elements dedicated to detecting vibrations, and four of said elements dedicated to excitation of the resonator.

Alternatively, each piezoelectric element10at the same time comprises a piezoelectric sub-element23capable of exciting the resonator in vibration and a piezoelectric sub-element24capable of detecting vibrations of the resonator, as illustrated inFIG. 5. In general, the sub-elements23,24are arranged near or adjacent to each piezoelectric element10.

Advantageously, the sub-elements23,24of the same piezoelectric element10are arranged on the same radius of the face5. They are generally distinct sub-elements23,24but arranged near one another.

In general, the sub-elements23,24are arranged on two concentric circles of different radii.

These can be distinct sub-elements, arranged near one from another, or contiguous zones of the same piezoelectric element.

In general, these are pellets, rectangular and metalized on their two faces, one of the face being stuck or brazed on the face of the resonator constituting the earth.

As explained earlier, the resonator is capable of vibrating according to a first vibration mode comprising antinodes distributed over two axes, and a second vibration mode comprising antinodes distributed over two other axes. They are elliptical vibration modes.

Advantageously, the face of the resonator comprises on each axis of the first and second vibration modes two piezoelectric elements10, each piezoelectric element10at the same time comprising at least one piezoelectric sub-element23capable of exciting the resonator in vibration and at least one piezoelectric sub-element24capable of detecting vibrations of the resonator.

This finally yields at least sixteen piezoelectric elements. This number can be limited to sixteen piezoelectric elements, with eight elements10each comprising two sub-elements23,24.

This is a major advantage for rejecting parasite modes occurring in the resonator, and multiplying the vibration measuring and control points, as explained hereinbelow.

In general, the gyroscope also comprises a protective cap, not shown, for retaining the vacuum created later under said cap and covering the assembly comprising the resonator and the base. The cap is for example a bell or a cylinder.

In an embodiment illustrated inFIG. 6, the face5comprises a central hole13. The resonator also comprises a linking foot21between the resonator3and the base2, arranged at the level of the extension of the central hole13. The foot is arranged inside the body of the resonator.

The foot21allows at least one electrical connection15to pass through, thus connecting the vibration control and processing modules18arranged in the base2and the piezoelectric elements23,24. The foot21likewise acts as mechanical linking between the resonator3and the base2, especially by way of its complementary form with a recess30of the base2.

This embodiment produces a highly compact gyroscope.

It is likewise possible to provide additional holes13in the face5, as mentioned earlier.

The invention also relates to a production process of a vibrating gyroscope1, such as described earlier. The process, illustrated inFIG. 7, comprises steps consisting of:providing a base2(step E1),forming a resonator3, comprising a body4of generally cylindrical form terminating in a distal face5, to the side opposite the base2, said face5comprising at least one through hole13(step E2),placing a plurality of piezoelectric elements10in contact with the resonator3, preferably on the face5(step E3),mechanically assembling the resonator3on the base2(step E4),placing, at least in part, vibration control and processing modules18in the base2(step E5), andelectrically connecting said modules18of the base2and the plurality of piezo-electrical elements10, via at least one electrical connection15passing through the interior of the body4of the resonator3via said hole13, for controlling and measuring the vibration of the resonator3(step E6).

In general, the resonator3is fixed on the base2by brazing.

In conventional terms, the process comprises a degassing step, and a step of vacuum sealing via the protective cap covering the assembly.

Because of the process according to the invention, the gyroscope is much easier to make, especially at the level of the electrical connections to be put in place, which can be made for example by a bonding process between the piezoelectric elements10and the interconnection card20.

FIG. 8illustrates an embodiment of the vibration control and processing in a gyroscope according to the invention.

This is especially completed by using vibration control and processing modules18, arranged at least in part in the base2. Of course, part of the modules18can be arranged outside the gyroscope1, for example on an electronic card placed near the gyroscope1.

In general, the vibration control and processing modules18are adapted to maintain the vibration of the resonator in cooperation with the piezoelectric elements10and for measuring the vibrations caused in the resonator. Most often, they comprise one or more electric signal generators, and electric modules such as amplifiers, filters, multipliers, adders, subtractors or the like.

The modules18are adapted to process the measured signal to deduce therefrom an angle of rotation and/or a speed of rotation about the axis z of the cylindrical body of the resonator3.

The modules18at the same time constitute a vibration excitation circuit and a detection/treatment circuit.

In general, the excitation circuit is in closed loop to give the excitation vibration of the resonator constant amplitude and a pulse equal to the pulse of the fundamental vibration mode.

It is understood that various embodiments of said modules are possible. Control and processing of vibration of the resonator of the cylinder are widely known from the prior art. Different types of execution are possible, for example: open-loop gyrometer mode, closed-loop gyrometer mode, and gyroscope mode.

FIG. 8illustrates an embodiment of control and processing of vibration of the resonator3in closed-loop gyrometer mode.

The gyroscope comprises eight piezoelectric elements10arranged between the holes of the face5of the resonator3. These elements are advantageously shaped as rectangular pellets distributed uniformly about the circumference of the face5of the resonator3.

An electrical signal generator25excites the piezoelectric elements10a,10e, arranged at the level of a first axis of antinodes of the first vibration mode of the resonator (axis x).

A measuring unit26receives the signals measured by the piezoelectric elements10c,10g, arranged at the level of a second axis of antinodes of the first vibration mode of the resonator (axis y).

The measuring unit26compares the amplitude of the first vibration mode to a set value and transmits to the generator25a deviation signal relative to this set point to modify the value of the vibration excitation signals and form amplitude slave control.

Rotation of the resonator causes a second elliptical vibration mode52whereof the main axes x1, y1are located at 45° from the axes x, y.

A measuring unit27receives the signals measured by the piezoelectric elements10b,10f, arranged at the level of a first axis of antinodes of the second vibration mode of the resonator (axis x1), arranged at 45° to the axes x,y.

When operating in closed loop, a processing unit28receives a signal from the measuring unit27representing the amplitude of the signals received by the measuring unit27, and deduces therefrom the excitation signals to be sent to the piezoelectric elements10d,10h, arranged at the level of a second axis of antinodes of the second vibration mode of the resonator (axis y1) to cancel out the amplitude of the signals detected by the measuring unit27. The measuring unit27deduces a signal representative of the angular speed of rotation Ω from the amplitude of these excitation signals.

FIG. 9shows another embodiment of control and processing of the vibration of the resonator.

Each of the piezoelectric elements10at the same time comprises a piezoelectric sub-element23capable of exciting the resonator in vibration and a piezoelectric sub-element24capable of detecting vibrations of the resonator.

The sub-elements23,24are advantageously shaped as rectangular pellets.

Alternatively, the sub-elements23and24can be made in the form of contiguous zones of the same element10.

The face5of the resonator3comprises on each axis of the first and of the second vibration mode two piezoelectric assemblies10, each piezoelectric assembly10at the same time comprising at least one piezoelectric sub-element23capable of exciting the resonator in vibration and at least one piezoelectric sub-element24capable of detecting vibrations of the resonator. The piezoelectric elements10are arranged on either side of the centre of the face of the resonator.

Here there are therefore sixteen piezoelectric elements23,24, eight in excitation and eight in measurements.

This embodiment rejects parasite vibration modes which might occur in the resonator, something not possible with only eight piezoelectric elements.

In general, for each vibration mode, the processing consists of getting a treated signal equal to the sum of the measurements of the piezoelectric sub-elements located on the antinodes showing amplitude of a given sign, minus the sum of the measurements of the piezoelectric sub-elements located on the antinodes showing amplitude of a sign opposite the given sign, said treated signal rejecting parasite vibration modes of the resonator. The sign of amplitudes of the antinodes (maxima of amplitude of vibration) is defined at one given instant of vibration, since the latter varies alternatively.

Of course, it is possible to generalise this embodiment in the event where the first and the second modes of vibration each exhibit antinodes distributed over n axes, and in this case each of the n axes comprises two piezoelectric elements10at the same time comprising at least one excitation sub-element element23at least one detection sub-element24.

The four piezoelectric sub-elements24a,24c,24eand24g, arranged according to the axes x,y of the antinodes of the first vibration mode, supply output signals each proportional to elongation of the vibration of the resonator and which are combined in a subtractor28to supply the input signal of a slave excitation circuit29of amplitude and phase.

The circuit shown by way of example comprises an amplifier30which attacks a multiplier31by way of a filter32piloted by a phase regulation chain.

The gain of the multiplier31is controlled by the amplitude regulation chain33which receives both the output signal of the amplifier30and a reference signal REF, representative of the amplitude to be maintained.

The filter32(active filter in general) is controlled for its part by a phase comparator40which receives both the output signal of the amplifier30and also the output signal of the circuit, coming from the multiplier31. The phase comparator40controls the filter32so as to maintain the phase difference at a constant value, generally zero.

The output signal of the circuit29attacks the piezoelectric sub-elements23a,23c,23e,23gby way of an inverter34, inverting the polarity of signals applied to the elements23cand23g.

The four piezoelectric sub-elements24b,24d,24f,24hsupply signals which are combined in a subtractor41to constitute the input signal of the measuring circuit42, in closed-loop gyrometer mode.

The circuit42can have a constitution of known type.

The circuit illustrated comprises an input amplifier43followed by a synchronous demodulator44which receives a reference signal constituted by an output signal of the circuit29.

The demodulated signal is applied to a low-pass filter45whereof the output46is representative of the angular rotation speed Ω. Looping in gyrometer mode is ensured by a link between the output of the amplifier43and the piezoelectric sub-elements23b,23d,23f,23h, by way of a modulator47, an amplifier48and an inverter49inverting the polarity of the signals applied to the elements23dand23h.

The subtractors28and41and inverters34and49can be dispensed with by appropriately orienting the polarisation vectors of the piezoelectric pellets23,24relative to each other.

As indicated earlier, the invention may have numerous variant embodiments, especially related to the constitution of the control and processing modules18linked to the mechanical resonator.

The person skilled in the art understands that the vibration control and processing modules18just now described are not limiting for the invention, and that various implementations and variants are possible.

As the person skilled in the art understands, the gyroscope according to the invention is more compact, simpler and less expensive to make. Also, it has a lower angular derive than some gyroscopes of the prior art (around 10°/H in some embodiments). Finally, the invention provides a gyroscope less sensitive to the vibratory environment, which is a major advantage.