PIEZOELECTRIC RING GYROSCOPE

Abstract

A ring gyroscope which comprises a substantially circular and flexible ring suspended from a substrate. The gyroscope comprises one or more primary piezoelectric split transducers placed on first sectors of the ring and one or more secondary piezoelectric split transducers placed on one or more second sectors of the ring. Each first sector crosses a transversal symmetry axis (T.sub.1, T.sub.2) of the ring and is symmetric with respect to that symmetry axis, and each second sector crosses a diagonal symmetry axis (D.sub.1, D.sub.2) of the ring and is symmetric with respect to that symmetry axis.

Claims

1. A ring gyroscope, comprising: a substantially circular and flexible ring which defines a ring plane, and which is flexibly suspended from a substrate so that the ring can undergo shape oscillation in the ring plane, wherein the ring comprises first and second transversal symmetry axes in the ring plane which are orthogonal to each other, and the ring also comprises first and second diagonal symmetry axes in the ring plane which are orthogonal to each other, and the angle between each transversal symmetry axis and the adjacent diagonal symmetry axis is 45°, wherein the gyroscope further comprises one or more primary piezoelectric split transducers placed on first sectors of the ring and one or more secondary piezoelectric split transducers placed on one or more second sectors of the ring, and each first sector crosses a transversal symmetry axis of the ring and is symmetric with respect to that symmetry axis, and each second sector crosses a diagonal symmetry axis of the ring and is symmetric with respect to that symmetry axis, and the gyroscope further comprises one or more tertiary piezoelectric split transducers on third sectors of the ring which do not overlap with the first sectors or the second sectors, wherein the one or more primary piezoelectric split transducers comprise a first pair of primary piezoelectric split transducers on two first sectors which cross the first transversal symmetry axis on opposite sides of the ring and a second pair of primary piezoelectric split transducers on two first sectors which cross the second transversal symmetry axis on opposite sides of the ring, and the one or more secondary piezoelectric split transducers comprise a first pair of secondary piezoelectric split transducers on two second sectors which cross the first diagonal symmetry axis on opposite sides of the ring and a second pair of secondary piezoelectric split transducers on two second sectors which cross the second diagonal symmetry axis on opposite sides of the ring.

2. The ring gyroscope according to claim 1, wherein the first pair of primary piezoelectric split transducers has a polarity-symmetry with respect to the center of the ring which is opposite to the polarity-symmetry of the second pair of primary piezoelectric split transducers with respect to the center of the ring.

3. The ring gyroscope according to claim 1, wherein the first pair of secondary piezoelectric split transducers has a polarity-symmetry with respect to the center of the ring which is opposite to the polarity-symmetry of the second pair of secondary piezoelectric split transducers with respect to the center of the ring.

4. The ring gyroscope according to claim 1, wherein the width of each first sector is less than 45°, and the width of each second sector is more than 45°.

5. The ring gyroscope according to claim 1, wherein the width of each first sector is more than 45°, and the width of each second sector is less than 45°.

6. The ring gyroscope according to claim 1, wherein the width of each first sector is less than 45°, and the width of each second sector is less than 45°.

7. A method for using a ring gyroscope, said method comprising: providing a ring gyroscope, the ring gyroscope comprising a substantially circular and flexible ring which defines a ring plane, and which is flexibly suspended from a substrate so that the ring can undergo shape oscillation in the ring plane, wherein the ring comprises first and second transversal symmetry axes in the ring plane which are orthogonal to each other, and the ring also comprises first and second diagonal symmetry axes in the ring plane which are orthogonal to each other, and the angle between each transversal symmetry axis and the adjacent diagonal symmetry axis is 45°, one or more primary piezoelectric split transducers placed on first sectors of the ring and one or more secondary piezoelectric split transducers placed on one or more second sectors of the ring, and each first sector crosses a transversal symmetry axis of the ring and is symmetric with respect to that symmetry axis, and each second sector crosses a diagonal symmetry axis of the ring and is symmetric with respect to that diagonal symmetry axis of the ring, wherein the one or more primary piezoelectric split transducers comprise a first pair of primary piezoelectric split transducers on two first sectors which cross the first transversal symmetry axis on opposite sides of the ring and a second pair of primary piezoelectric split transducers on two first sectors which cross the second transversal symmetry axis on opposite sides of the ring, and the one or more secondary piezoelectric split transducers comprise a first pair of secondary piezoelectric split transducers on two second sectors which cross the first diagonal symmetry axis on opposite sides of the ring and a second pair of secondary piezoelectric split transducers on two second sectors which cross the second diagonal symmetry axis on opposite sides of the ring, and the ring gyroscope also comprises one or more tertiary piezoelectric split transducers on third sectors of the ring which do not overlap with the first sectors or the second sectors; further comprising applying to at least one primary piezoelectric split transducer a drive voltage signal to generate the primary oscillation mode in the ring gyroscope; and reading from at least one secondary piezoelectric split transducer a sense voltage signal to measure the oscillation amplitude of secondary oscillation in the ring gyroscope.

8. The method according to claim 7, wherein the method also comprises reading from at least one primary piezoelectric split transducer a third voltage signal to measure the oscillation amplitude of primary oscillation in the ring gyroscope.

9. The method according to claim 7, wherein the method also comprises applying to at least one secondary piezoelectric split transducer a fourth voltage signal to actively cancel the coupling of the primary oscillation into the secondary oscillation.

10. The method according to claim 7, wherein the method also comprises reading from at least one tertiary piezoelectric split transducer a fifth voltage signal to measure the oscillation amplitude of primary oscillation in the ring gyroscope.

11. The method according to claim 7, wherein the method also comprises applying to at least one tertiary piezoelectric split transducer a sixth voltage signal to actively cancel the coupling of the primary oscillation into the secondary oscillation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In the following the disclosure will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which

[0020] FIG. 1 illustrates the primary and secondary modes in an oscillating ring gyroscope.

[0021] FIG. 2 illustrates three cross-sections of a bending piezoelectric transducer placed on a gyroscope ring.

[0022] FIG. 3 illustrates the variation of tangential stress along the inner and outer perimeters of a gyroscope ring.

[0023] FIG. 4 illustrates a ring gyroscope.

[0024] FIG. 5 illustrates a ring gyroscope.

[0025] FIG. 6 illustrates a ring gyroscope.

[0026] FIG. 7 illustrates a ring gyroscope.

[0027] FIG. 8 illustrates a ring gyroscope.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0028] FIG. 2 illustrates three cross-sections of a bending piezoelectric transducer placed on a gyroscope ring. The transducer can generate or measure bending motion in the xy-plane. A pair of first electrode layers 241 and 242 have been placed on silicon ring 21, one on the upper side of a layer of piezoelectric material 22 and one on the lower side (up and down refers in this case to the direction of the z-axis). These electrodes are paired with second electrode layers 231 and 232, respectively, as illustrated in the figure. Layers 241, 22 and 231 together form a first piezoelectric transducer on top of the ring 21, and layers 242, 22 and 232 together form a second piezoelectric transducer on top of the ring 21.

[0029] If drive voltages with opposite polarity are applied to these two transducers, the two transducers produce opposite strains in the xy-plane, which can deform silicon ring 21. If the transducers are used as sense transducers, in-plane bending will generate a voltage differential between the two transducers.

[0030] The drawing conventions of FIG. 2 will be employed throughout this disclosure to illustrate piezoelectric transducers. In other words, two parallel rectangles of opposite colour will be used to indicate a piezoelectric transducer. For simplicity, these two parallel rectangles will primarily be referred to in the singular, as a single “split transducer”, even though the structure is actually a construction which comprises two transducers. In other words, a split transducer must comprise two parallel transducers.

[0031] Black and white colours indicate transducer polarity. The ordering of the black and white rectangles in a split transducer indicate polarity so that the polarity of a transducer with a white rectangle on the outer side of the ring is opposite to the polarity of a transducer with a black rectangle on the black rectangle on the outside of the ring (as seen in the same figure).

[0032] The piezoelectric layer 22, which may be an aluminium nitride (AlN) layer, is typically not thicker than a few micrometers. The thickness of the silicon ring 21 may, for example, be between 4-100 μm, preferably between 10-50 μm.

[0033] When piezoelectric transducers described in this disclosure are used in the sense mode, the largest output voltage between the electrodes of the transducer may be achieved when the transducer capacitance equals the sum of the capacitance of the external connections and the input capacitance of the amplifier. The capacitance of the transducer is determined by its area and by the thickness of the piezoelectric layer.

[0034] Due to the narrowness of a gyroscope ring, certain design tradeoffs have to be made when piezoelectric transducers are fabricated on the top surface of the ring. A practical split electrode transducer requires at least 15 μm, preferably at least 20 μm of width. But if, for example, one would wish to fabricate a ring gyro with 30 kHz resonant frequency and 1 mm diameter, the ring width has to be less than 7 μm, which is too narrow for split transducers.

[0035] In order to implement piezoelectric transduction on basic gyroscope ring, the width of the ring must be increased. This increases the resonance frequency. A ring width of 15 μm increases the resonant frequency to 67 kHz. But even this may be too narrow, because the total maximum capacitance of a 15 μm wide split transducer with a 1 μm AlN layer is only 3,7 pF, which will be shared with many functions in addition to sensing the secondary oscillation: e.g. driving the primary oscillation, sensing the magnitude of the primary oscillation and driving a compensating signal in the secondary mode to cancel the secondary oscillation in a closed feed-back loop and/or damping the secondary resonance and/or cancelling the quadrature signal. For perfect match to the surrounding electronics, the total capacitance should preferably be 7-15 pF since it is not easy to use more than 50% of the maximum capacitance for sensing the secondary oscillation.

[0036] Increasing ring width to 30 μm makes the capacitance 7.6 pF, but the corresponding resonance frequency is then 140 kHz. At high frequency operation the gyroscope becomes more immune to external vibrations, which are predominantly at lower frequencies, but the quadrature signal due to direct mechanical coupling of the primary mode to the transducers which should measure only the secondary mode will also increase with frequency. The desired signal-to-noise ratio may therefore have to be weighed against the required quadrature compensation at a given resonance frequency. The ring width may, for example, be 15-30 μm, 15-25 μpm or 15-20 μm.

[0037] An obvious way to increase the width of the ring and the capacitance without increasing the resonant frequency too much is to increase the diameter of the ring. If the diameter is chosen to be 1.6 mm and the width 18 μm, the resonant frequency will be 31 kHz and the capacitance 7.2 pF, numbers which are close to an ideal target. But this gyroscope will have 2.5 times as large area as a 1 mm diameter gyroscope and thus 2.5 times the manufacturing costs of the 1 mm diameter gyroscope.

[0038] The primary and secondary oscillation modes produce mechanical stress on the inner and outer perimeter of the ring. The momentary stress varies as a sinusoidal function of length along the ring perimeter. The length variable is in this case represented by the clockwise angle with respect to the T.sub.2-axis pointing in the positive y-direction in FIG. 1. FIG. 3 shows the variation of tangential stress along the inner and outer perimeters of the ring for both oscillation modes. At the illustrated moment, the stress varies as a cosine-function of the angle for the primary mode and as a sine-function for the secondary mode, and the stress on the inner perimeter is in each case equal but opposite to the stress on the outer perimeter. As a function of time the amplitudes of the stresses of FIG. 3 will vary proportional to sin(ωt), where ω is the angular frequency of the oscillation. The angular distribution along the perimeter of the ring will remain same independent of time. This stress distribution can be generated and detected by piezoelectric split transducers positioned on the top surface of the ring and lengthwise along the perimeter of the ring. A split transducer positioned on the ring for driving the primary oscillation will produce opposite and constant stress on each perimeter of the ring.

[0039] This disclosure describes a ring gyroscope which comprises a substantially circular and flexible ring which defines a ring plane, and which is flexibly suspended from a substrate so that the ring can undergo shape oscillation in the ring plane. The ring comprises first and second transversal symmetry axes in the ring plane which are orthogonal to each other. The ring also comprises first and second diagonal symmetry axes in the ring plane which are orthogonal to each other. The angle between each transversal symmetry axis and the adjacent diagonal symmetry axis is 45°.

[0040] The gyroscope further comprises one or more primary piezoelectric split transducers placed on first sectors of the ring, and one or more secondary piezoelectric split transducers placed on one or more second sectors of the ring. Each first sector crosses a transversal symmetry axis of the ring and is symmetric with respect to that symmetry axis. Each second sector crosses a diagonal symmetry axis of the ring and is symmetric with respect to that diagonal symmetry axis of the ring.

[0041] In this disclosure, expressions such as “a piezoelectric split transducer placed on sector A of the ring” always mean that a piezoelectric split transducer is placed on top of the ring in sector A of the ring. FIG. 2 illustrates how split transducers may be placed on top of the ring.

[0042] This disclosure also describes a method for using a ring gyroscope described above, wherein the method comprises the steps of: applying to at least one primary piezoelectric split transducer a drive voltage signal to generate the primary oscillation mode in the ring gyroscope, and reading from at least one secondary piezoelectric split transducer a sense voltage signal to measure the oscillation amplitude of secondary oscillation in the ring gyroscope. The same method can be employed with any ring gyroscope described in this disclosure.

[0043] FIG. 4 illustrates a ring gyroscope which comprises a ring 42. The planar ring defines the ring-plane which corresponds to the xy-plane in FIG. 4. The suspension arrangement is not illustrated. The first and second transversal symmetry axes T.sub.1 and T.sub.2, and the first and second diagonal symmetry axes D.sub.1 and D.sub.2 correspond to the symmetry axes discussed above with reference to FIG. 1. At least one primary piezoelectric split transducer 411 has been placed on the ring 42. This split transducer 411 covers a first sector of the ring which corresponds to the angle α, as illustrated in FIG. 4. The midpoint of this sector (or, equivalently, the midpoint of the transducer 411) defines the direction of first transversal symmetry axis T.sub.1. An alternating drive voltage applied to split transducer 411 will alternately stretch and compress the ring 42 along transversal symmetry axis T.sub.1.

[0044] In other words, since a circle has infinitely many symmetry axes, the direction of the first symmetry axis can be freely selected by the placement of the first primary split transducer 411. Once the first axis T.sub.1 has been defined, the other three symmetry axes T.sub.2, D1 and D.sub.2 have also already been uniquely defined, and the placement of subsequent primary and secondary split transducers on the ring must conform to the following requirements: [0045] 1. A second primary piezoelectric split transducer 412 may optionally be placed opposite to 411, on the other side of the ring. The midpoint of this second primary split transducer 412 must lie as close as possible to the first transversal symmetry axis T.sub.1. In other words, split transducer 412 defines another first sector of the ring which must cross the transversal symmetry axis T.sub.1 of the ring and be symmetric with respect to that axis. In this context, symmetry means that the sector extends equally far on both sides of the axis T.sub.1. Since the second split transducer 412 illustrated in FIG. 4 has the same polarity symmetry with respect to the center of the ring as the first split transducer 411, the drive voltage signal applied to transducer 412 should have the same phase as the drive voltage signal applied to transducer 411. The drive oscillations induced by these two split transducers will then reinforce each other. If the polarity of the second split transducer 412 with respect to the center of the ring would be opposite to the polarity of transducer 411, the drive voltage signals should exhibit a phase difference of 180°. [0046] 2. Third and fourth primary piezoelectric split transducers 413 and 414 may optionally be placed on opposite sides of the ring. Their positions are shifted from the positions of first and second primary piezoelectric split transducers 411 and 412 by 90°. The midpoints of these third and fourth primary split transducers 413 and 414 must lie as close as possible to the second transversal symmetry axis T.sub.2. In other words, split transducers 413 and 414 define additional first sectors of the ring which must cross the transversal symmetry axis T.sub.2 of the ring and be symmetric with respect to that axis. Since the third and fourth split transducer 413 and 414 illustrated in FIG. 4 have the opposite polarity symmetry with respect to the center of the ring as the first split transducer 411, the drive voltage signal applied to split transducers 413 and 414 should have the same phase as the drive voltage signal applied to transducer 411. The ring will then be driven to contract along axis T.sub.2 when it expands along axis T.sub.1, and vice versa. If either one or both of split transducers 413 and 414 would have the same polarity as 411, then that transducer can be driven with a drive voltage signal which has been shifted 180° in relation to the signal applied to transducer 411. [0047] 3. One to four secondary piezoelectric split transducers 431-434 may be placed on fours sides of the ring, each shifted from the adjacent secondary split transducers by an angle of 90°. The midpoints of these secondary split transducers 431-434 must lie as close as possible to the either the first diagonal symmetry axis D.sub.1 or the second diagonal symmetry axis D.sub.2. As explained above, these diagonal symmetry axes are shifted from the transversal symmetry axes by an angle of 45°. Each secondary split transducer 431-434 defines a second sector of the ring. Each second sector must cross a diagonal symmetry axis of the ring and be symmetric with respect to that axis. As before, symmetry in this context means that the sector extends equally far on both sides of the diagonal symmetry axis. The polarity of the secondary split transducers with respect to the center of the ring may be chosen freely. FIG. 4 illustrates the simplest alternative where the polarity of secondary split transducers 431 and 432, which cross the first diagonal symmetry axis D.sub.1, is opposite to the polarity of secondary split transducers 433 and 434, which cross the second diagonal symmetry axis D.sub.2. Since expansion along D.sub.1 is always accompanied by contraction along D.sub.2 and vice versa, the sense voltages obtained from all secondary split transducers 431-434 can in this case be joined directly together.

[0048] In other words, at least one primary piezoelectric split transducer should be present on the ring to excite the primary resonance motion of the ring. This excitation is achieved by applying an alternating voltage to the primary piezoelectric split transducer, with a frequency which is equal or close to the resonance frequency of the ring. The primary piezoelectric split transducers should preferably be placed symmetrically in relation to a transversal symmetry axis of the ring.

[0049] Additionally, at least one secondary piezoelectric split transducer should be present on the ring to detect the oscillation coupled by the Coriolis force when the ring rotates about its central axis which is perpendicular to the ring plane. The secondary piezoelectric split transducers should preferably be placed symmetrically in relation to a diagonal symmetry axis of the ring.

[0050] Misalignment of any first or second sector (i.e. any primary or secondary transducer) will induce unwanted coupling of primary oscillation into the secondary oscillation mode. This is a because a misaligned primary transducer 411-414 will generate oscillation which puts the adjacent nodal point 44 in motion, even though the nodal points 44 should remain stationary when the ring oscillates only in the primary resonance mode. The oscillation of the nodal point 44 will be picked up by secondary split transducers 431-434 and create an erroneous sense signal. Conversely, a misaligned secondary transducer will be centered at a point which differs from the nodal point 44, which also leads it to pick up the primary resonance oscillation and to produce an erroneous sense signal. If, on the other hand, all primary and secondary split transducers are perfectly aligned, then secondary split transducers 431-434 will only pick up the true secondary resonance mode, which is the oscillation of nodal points 44 induced by the Coriolis force.

[0051] A single primary piezoelectric split transducer on a first sector of the ring and a single secondary split transducer on a second sector of the ring is sufficient for operating the ring gyroscope. However, to improve the signal-to-noise ratio and reduce the possibility of errors due to misalignment, the number of both primary and secondary split transducers may be increased according to geometry illustrated as illustrated in FIG. 4.

[0052] In other words, the gyroscope may comprise a first pair of primary piezoelectric split transducers 411, 412 on two first sectors which cross the first transversal symmetry axis T.sub.1 on opposite sides of the ring 42. Optionally, the gyroscope may also comprise a second pair of primary piezoelectric split transducers 413, 414 on two first sectors which cross the second transversal symmetry axis T.sub.2 on opposite sides of the ring 42. The first pair of primary piezoelectric split transducers 411, 412 may have a polarity-symmetry with respect to the center of the ring 42 which is opposite to the polarity-symmetry of the second pair of piezoelectric split transducers 413, 414 with respect to the center of the ring 42.

[0053] Furthermore, the gyroscope may comprise a first pair of secondary piezoelectric split transducers 431, 432 on two second sectors which cross the first diagonal symmetry axis D.sub.1 on opposite sides of the ring 42. Optionally, the gyroscope may also comprise a second pair of secondary piezoelectric split transducers 433, 434 on two second sectors which cross the second diagonal symmetry axis D.sub.2 on opposite sides of the ring 42. The first pair of secondary piezoelectric split transducers 431, 432 may have a polarity-symmetry with respect to the center of the ring 42 which is opposite to the polarity-symmetry of the second pair of secondary piezoelectric split transducers 433, 434 with respect to the center of the ring 42.

[0054] In the ring gyroscope illustrated in FIG. 4, the width of each first sector and each second sector is 45°. In other words, the length of each primary split transducer 411-414 and the length of each secondary split transducer 431-433 is equal to ⅛ of the ring circumference. In FIG. 4, where there are eight split transducers in total, the primary and secondary split transducers together cover the entire circumference of the ring. This maximizes the force obtained from the primary transducers and the sense signal strength obtained from the secondary transducers.

[0055] However, sometimes some of the area on the top surface of the ring may be needed for other purposes than force transduction, for example drive amplitude monitoring, coupling cancellation or electrical contacting.

[0056] FIG. 5 illustrates a ring gyroscope according to another embodiment. Reference numbers 511-514, 531-534, 52 and 54 correspond to reference numbers 411-414, 431-434, 42 and 44, respectively in FIG. 4. In FIG. 5, the width of each first sector is less than 45°, and the width of each second sector is less than 45°. For illustrative purposes the length of each transducer is 1/16 of the ring circumference, so that the corresponding width of each first and second sector is 22.5°, but transducer lengths can be selected freely. The symmetry criterion remains the same as in FIG. 4: each first and second sector should be symmetric with respect to the symmetry axis which it crosses. Deviations from this symmetry will cause unwanted coupling of primary mode oscillation into the secondary mode, as described above.

[0057] FIG. 6 illustrates an alternative embodiment where the width of all first sectors is less than 45°, the width of two second sectors is less than 45°, and the width of the two other second sectors is more than 45°. Reference numbers 611-614, 631-634, 62 and 64 correspond to reference numbers 511-514, 531-534, 52 and 54, respectively, in FIG. 5. Alternatively, the width of each first sector may be less than 45°, and the width of each second sector may be more than 45°. These configurations, which open up some room on the ring surface by narrowing the first sectors, can be advantageous when driving force can be sacrificed but sense signal strength cannot.

[0058] The force required for driving the primary oscillation depends on the dimensions of the ring, the length of the primary transducers and the amplitude of the drive voltage signal applied to these primary transducers. As before, each first and second sector must still be symmetric with respect to the symmetry axis which it crosses.

[0059] Alternatively, the width of each first sector may be more than 45°, and the width of each second sector may be less than 45°. This configuration can be advantageous when the driving force must be maximized, but some of the sense signal strength can be sacrificed. This option is not separately illustrated, but it corresponds directly to FIG. 6, except that each primary split transducer would cover more than ⅛ of the ring circumference, while no secondary split transducer would cover more than ⅛ of the circumference.

[0060] All primary split transducers do not necessarily have to be used for driving the primary oscillation. Some of them may, for example, be used for measuring the amplitude of the primary oscillation. This is needed for maintaining stable oscillation amplitude independent of the changes in the driving frequency or the Q-value of the resonator due to environmental variables or aging.

[0061] In other words, a method for using any ring gyroscope described in this disclosure may comprise the step of reading from at least one primary piezoelectric split transducer a third voltage signal to measure the oscillation amplitude of primary oscillation in the ring gyroscope.

[0062] Similarly, all secondary split transducers do not necessarily have to be used for measuring the secondary oscillation. Some of them may, for example, be used for active interventions into the secondary oscillation mode. For example, when the ring gyroscope is used in closed-loop servo mode, or when the secondary mode resonance is damped by closed loop feedback, or when an applied electromechanical force is used to cancel a quadrature signal, at least one secondary piezoelectric split transducer may be driven with an alternating voltage so that it actively cancels the coupling of the primary oscillation into the secondary oscillation. The lengths of the secondary transducers which are dedicated to active cancelling may differ from the lengths of the secondary transducers which sense the secondary oscillation.

[0063] In other words, a method for using any ring gyroscope described in this disclosure may comprise the step of applying to at least one secondary piezoelectric split transducer a fourth voltage signal to actively cancel the coupling of the primary oscillation into the secondary oscillation.

[0064] If the primary and secondary split transducers do not together cover the entire circumference of the ring, the vacant surface area (for example, the unused area on the ring in FIGS. 5 and 6) can be used for other purposes. FIG. 7 illustrates an alternative embodiment where reference numbers 711-714, 731-734, 72 and 74 correspond to reference numbers 611-614, 631-634, 62 and 64, respectively, in FIG. 6. In this embodiment, the width of at least one first or second sector is less than 45°. The gyroscope comprises one or more tertiary piezoelectric split transducers on third sectors of the ring, which do not overlap with the first sectors or the second sectors.

[0065] Eight tertiary piezoelectric split transducers 751-758 are illustrated in FIG. 7. The number of tertiary piezoelectric split transducers could be smaller, and it may depend on the widths of the primary and secondary transducers. The number of tertiary piezoelectric split transducers may also be larger than eight. Several third sectors may fit between first and second sectors.

[0066] One or more of the tertiary piezoelectric transducers 751-758 may be used for detecting the amplitude of the primary oscillation. This amplitude may not remain constant during the lifetime of the device due to temperature stress and other aging effects. Drift in the drive amplitude will immediately introduce a proportional error in the sensed amplitude, but this error can be corrected if the primary oscillation is monitored.

[0067] In other words, a method for using a ring gyroscope which comprises one or more tertiary piezoelectric split transducers on third sectors of the ring which do not overlap with the first sectors or the second sectors may comprise the step of reading from at least one tertiary piezoelectric split transducer a fifth voltage signal to measure the oscillation amplitude of primary oscillation in the ring gyroscope.

[0068] One or more of the tertiary piezoelectric transducers 751-758 may also be used for cancelling coupled oscillation when the gyroscope is used in closed loop servo mode or when the secondary resonance mode is actively damped by closed-loop feedback, or when electromechanical force is used to cancel a quadrature signal, as described above.

[0069] In other words, a method for using a ring gyroscope which comprises one or more tertiary piezoelectric split transducers on third sectors of the ring which do not overlap with the first sectors or the second sectors may comprise the step of applying to at least one tertiary piezoelectric split transducer a sixth voltage signal to actively cancel the coupling of the primary oscillation into the secondary oscillation.

[0070] FIG. 8 illustrates an alternative embodiment where reference numbers 811-814, 831-834, 855-856, 82 and 84 correspond to reference numbers 711-714, 731-734, 755-756, 72 and 74, respectively, in FIG. 7. In this embodiment, three of the secondary transducers on the second sectors, 831-833, have a width larger than 45°, and the fourth one, 834, has a width less than 45°. All of these secondary transducers are used for detecting the secondary oscillation. All transducers on the primary sectors, 811-14, have a width less than 45°, and they are used for exciting the primary oscillation. There are only two tertiary transducers on third sectors, 855 and 856. One of these tertiary transducers is used for detecting the amplitude of the primary oscillation, as described above. The other is used for cancelling coupled oscillation when the gyroscope is used in closed loop servo mode or when the secondary resonance mode is actively damped by closed-loop feedback, or when electromechanical force is used to cancel a quadrature signal, as described above.

[0071] As indicated visually in FIG. 8, the whole perimeter of the ring may be fully covered by transducers for the described functions. The gyroscope may be optimized by selecting optimum transducer lengths for each function, so that sufficiently high signal-to-noise ratios are obtained for the primary and secondary signals, while keeping the voltages for driving the primary oscillation and for cancelling coupled oscillation suitably low.