Gyroscope system, inertial measuring unit, and method of operating angular rate sensor

Abstract

To provide an improved gyroscope system.SOLUTION: A gyroscope system includes at least one vibrating structure gyroscope having: a structure; one or more drive transducers configured to drive the structure; and one or more pick-off transducers configured to detect oscillation of the structure. The vibrating structure gyroscope is configured to operate in a sensing mode or a diagnostic mode. The vibrating structure gyroscope is configured, during the sensing mode, to measure an angular rate of rotation of the vibrating structure gyroscope. The system also includes a controller configured to operate the vibrating structure gyroscope in the diagnostic mode such that the one or more drive transducers drive the structure at a frequency other than a resonant frequency of the structure.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to gyroscope systems. [Background technology]

[0002] A gyroscope system includes a vibrating gyroscope (VSG) that measures angular rate. However, rate output errors occur due to bias errors in the device components. Therefore, it is desirable to improve gyroscope systems, particularly to reduce errors in the measured angular rate.

[0003] One particularly problematic bias error in these devices is crosstalk bias (also called pickup bias), which arises primarily due to direct coupling of the primary drive signal into the secondary pick-off signal. This coupling is indistinguishable from the applied rotation rate and therefore manifests itself as a spurious bias output that reduces the accuracy of the device. Therefore, a means is needed to measure and virtually eliminate this error. Summary of the Invention [Problem to be solved by the invention]

[0004] SUMMARY OF THE PRESENT EMBODIMENT It is therefore an object of the present invention to improve gyroscope systems such that the above mentioned disadvantages are reduced. [Means for solving the problem]

[0005] According to one aspect, a gyroscope system is provided that includes at least one vibratory gyroscope comprising a structure, one or more drive transducers configured to drive the structure, and one or more pick-off transducers configured to detect vibrations of the structure, the vibratory gyroscope configured to operate in a sensing mode or a diagnostic mode, and configured to measure a rotational angular rate of the vibratory gyroscope during the sensing mode, and a controller configured to operate the vibratory gyroscope in the diagnostic mode such that the one or more drive transducers drive the structure at a frequency other than a resonant frequency of the structure. By driving the vibratory gyroscope at the non-resonant frequency in the diagnostic mode, errors in the output of the vibratory gyroscope can be identified and eliminated.

[0006] The controller may be configured to operate the vibratory gyroscope in a diagnostic mode to identify one or more pickoff bias errors of the vibratory gyroscope.

[0007] The controller may be configured to receive one or more diagnostic pickoff transducer signals from the vibratory gyroscope when operating the vibratory gyroscope in the diagnostic mode, and to identify one or more pickoff bias errors of the vibratory gyroscope based on the one or more diagnostic pickoff transducer signals.

[0008] The controller may be configured to correct an output of the vibratory gyroscope based on one or more pickoff bias errors of the vibratory gyroscope when operating the vibratory gyroscope in the sensing mode.

[0009] The controller may be configured to switch the vibratory gyroscope from operating in a diagnostic mode to operating in a sensing mode or from operating in a sensing mode to operating in a diagnostic mode. The controller may be configured to suppress vibrations of the structure when the vibratory gyroscope is switched from operating in the sensing mode to operating in the diagnostic mode.

[0010] The controller may be configured to receive one or more sensing pickoff transducer signals from the vibratory gyroscope when operating the vibratory gyroscope in the sensing mode, and may be configured to correct an output of the vibratory gyroscope by subtracting one or more pickoff bias errors of the vibratory gyroscope from the one or more sensing pickoff transducer signals when operating the vibratory gyroscope in the sensing mode.

[0011] The one or more drive transducers may be configured to drive the structure such that vibrations of the structure are not generated when operating the vibratory gyroscope in the diagnostic mode.

[0012] The controller may be configured to determine a ratio between a drive signal of the one or more drive transducers when operating the vibratory gyroscope in a sensing mode and a drive signal of the one or more drive transducers when operating the vibratory gyroscope in a diagnostic mode.

[0013] The controller may be configured to determine one or more pickoff bias errors by multiplying the ratio by one or more diagnostic pickoff transducer signals.

[0014] The diagnostic pick-off transducer signal(s) may be a magnitude of coupling between the drive transducer(s) and the pick-off transducer(s).

[0015] The one or more drive transducers may include one or more primary and / or secondary drive transducers. The one or more pick-off transducers may include one or more primary and / or secondary pick-off transducers.

[0016] The gyroscope system may include an additional vibratory gyroscope having a structure, one or more drive transducers configured to drive the structure, and one or more pick-off transducers configured to detect vibrations of the structure, where the additional vibratory gyroscope is configured to operate in a sensing mode or a diagnostic mode, and where the additional vibratory gyroscope is configured to measure a rotational angular rate of the vibratory gyroscope during the sensing mode.

[0017] The controller may be configured to operate one of the vibratory gyroscopes in a diagnostic mode while the other vibratory gyroscope operates in a sensing mode, thereby allowing errors in one of the vibratory gyroscopes to be corrected while the gyroscope system is in operation.

[0018] The controller may be configured to cycle through the vibratory gyroscopes such that each vibratory gyroscope is operated in a diagnostic mode at least once while the other vibratory gyroscope is operating in a sensing mode.

[0019] The gyroscope system may include a total of four vibratory gyroscopes, each having a structure, one or more drive transducers configured to drive the structure, and one or more pick-off transducers configured to detect vibrations of the structure, each vibratory gyroscope configured to operate in a sensing mode or a diagnostic mode, and each vibratory gyroscope configured to measure a rotational angular rate of the vibratory gyroscope during the sensing mode.

[0020] The vibratory gyroscopes may be arranged in a tetrahedral shape.

[0021] The controller may be configured to operate at least one of the vibratory gyroscopes in a diagnostic mode while one or more of the other three vibratory gyroscopes are operating in a sensing mode, such that errors in one of the vibratory gyroscopes can be corrected while the gyroscope system is operating.

[0022] The controller may be configured to cycle through the vibratory gyroscopes such that each vibratory gyroscope is operated in a diagnostic mode at least once while one or more of the other three vibratory gyroscopes are operating in a sensing mode.

[0023] According to a second aspect, there is provided an inertial measurement unit including a gyroscope system as described above.

[0024] According to a third aspect, there is provided a method of operating an angular rate sensor including at least one vibratory gyroscope having a structure, one or more drive transducers configured to drive the structure, and one or more pick-off transducers configured to detect vibrations of the structure, the vibratory gyroscope configured to operate in a sensing mode or a diagnostic mode, the vibratory gyroscope configured to measure a rotational angular rate of the vibratory gyroscope during the sensing mode, the method including operating the vibratory gyroscope in the diagnostic mode such that the one or more drive transducers drive the structure at a frequency other than a resonant frequency of the structure.

[0025] The embodiments will be further described and explained, by way of example, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0026] [Figure 1] 1 shows a schematic diagram of a gyroscope system. [Diagram 2] 1 shows a schematic diagram of a gyroscope system. [Diagram 3] A method for operating the gyroscope system is shown. [Figure 4] 1 shows a schematic diagram of a gyroscope. [Diagram 5] 1 shows a schematic diagram of a gyroscope system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] 1, the gyroscope system 100 includes a vibratory gyroscope 110 and a controller 160. The controller 160 is configured to operate the vibratory gyroscope 110 in a sensing mode or a diagnostic mode.

[0028] The vibratory gyroscope 110 includes a structure 111 coupled to a primary drive transducer 112, a primary pick-off transducer 113, and a secondary pick-off transducer 114. The primary drive transducer 112 drives the structure 111 in a first position, and the primary and secondary pick-off transducers 113, 114 output signals in response to the primary drive transducer 112 driving the structure 111. The primary drive transducer 112, the primary pick-off transducer 113, and / or the secondary pick-off transducer 114 may be one of an inductive transducer, a capacitive transducer, or a piezoelectric transducer.

[0029] 1, the structure 111 is a planar ring. However, in alternative embodiments, the structure 111 may include one or more of a ring, a beam, a tuning fork, a cylinder, a hemispherical shell, and a disk.

[0030] When the vibratory gyroscope 110 is operating in a sense mode, the primary drive transducer 112 receives a primary sense drive signal at the resonant frequency of the structure 111. This causes the primary drive transducer 112 to drive the structure 111 into vibration, forming a radial antinode (i.e., the location of maximum vibration of the structure 111) at the location of the primary drive transducer 112.

[0031] The primary pick-off transducer 113 senses the radial vibration of the structure 111 at a location 90° from the primary drive transducer 112 where the second radial antinode is formed and outputs a primary sense pick-off transducer signal to an amplitude control loop 118. This signal is received by a primary pick-off amplifier 117 which amplifies the signal and then provides the amplified signal to a frequency control loop 119.

[0032] A phase locked loop 120 adjusts the phase of the amplified signal and a voltage controlled oscillator 121 adjusts the frequency of the amplified signal to maintain resonant vibration of the structure 111. The adjusted signal is then sent to the primary drive amplifier 116 where the signal is amplified before being provided to the primary drive transducer 112 as the primary sense drive signal.

[0033] The primary pickoff amplifier 117 also provides an amplified signal to an automatic gain control circuit 122, which adjusts the gain of the primary drive amplifier 116 to ensure that the amplitude of the primary sensing pickoff transducer signal is constant.

[0034] 1, amplitude control loop 118 includes primary pickoff amplifier 117, automatic gain control circuit 122, and primary drive amplifier 116. Frequency control loop 119 includes phase locked loop 120 and voltage controlled oscillator 121. Together, amplitude control loop 118 and frequency control loop 119 form primary loop 123.

[0035] The secondary pick-off transducer 114 is placed at a radial node of the structure 111 (i.e., at a point where the structure 111 is stationary and is not expected to vibrate radially when the primary drive transducer 112 vibrates the structure 111 at its resonant frequency). As the vibratory gyroscope 110 rotates about its axis, the Coriolis force causes the radial antinodes and nodes to move location on the structure 111. When this occurs while the vibratory gyroscope 110 is operating in a sense mode, the secondary pick-off transducer 114 detects a radial vibration at a node (where it was not before) and outputs a secondary sense pick-off transducer signal to the secondary loop 124. This signal is received by the secondary pick-off amplifier 125, which amplifies the signal.

[0036] The amplified signal includes both a "real" component (i.e., a sine component) and a "quadrature" component (i.e., a cosine component). The "real" component provides the rotation angular rate of the vibratory gyroscope 110, and the "quadrature" component is an error generated by system imperfections. The "quadrature" component is in phase orthogonal to the "real" component and therefore does not contribute to the rotation angular rate. Therefore, in an open-loop configuration, the amplified signal can pass through the first demodulator 126 to extract the "real" component and thus the rotation angular rate of the vibratory gyroscope 110 output from the vibratory gyroscope 110.

[0037] Note that structure 111 also vibrates tangentially, however this tangential vibration is typically not detected by primary pickoff transducer 112 or secondary pickoff transducer 114 and therefore does not affect the output of vibratory gyroscope 110.

[0038] 1, in a closed loop configuration, the vibratory gyroscope 110 further comprises a secondary drive transducer 115. Like the secondary pickoff transducer 114, the secondary drive transducer 115 is located at a radial node of the structure 111 (i.e., at a point where the structure 111 is at rest and is not expected to vibrate radially when the primary drive transducer 112 vibrates the structure 111 at its resonant frequency).

[0039] The amplified signal from the secondary pickoff amplifier 125 passes through a second demodulator 127 to extract the "quadrature" component. The "real" and "quadrature" components are then recombined and amplified by a secondary drive amplifier 128 to produce a secondary sense drive signal. This secondary sense drive signal is received by the secondary drive transducer 115, which causes the secondary drive transducer 115 to null out vibrations at the radial nodes.

[0040] In this embodiment, the amplitude of the secondary sense drive signal is output from vibratory gyroscope 110 and is proportional to the rotational angular rate of vibratory gyroscope 110 .

[0041] As shown in FIG. 1, secondary loop 124 includes a secondary pickoff amplifier 125 , a first demodulator 126 , and, optionally, a second demodulator 127 and a secondary drive amplifier 128 .

[0042] The "quality factor" (often referred to as "Q factor" or simply "Q") of structure 111 is a measure of the quality of the resonance achieved by structure 111. A high Q means that there is relatively low damping and that structure 111 will vibrate at the resonant frequency with a relatively high amplitude for a relatively long time. On the other hand, a low Q means that there is relatively high damping such that the vibrations decay more quickly. In general, a high Q is desirable for a vibratory gyroscope.

[0043] When the vibratory gyroscope 110 operates in a sense mode, the amplitude of the primary sense drive signal of the primary drive transducer 112 is set to achieve a radial vibration with a large amplitude. This allows the primary sense drive signal to couple to the primary sense pick-off transducer signal and the secondary sense pick-off transducer signal by capacitive or inductive mechanisms. Such coupling may occur in the structure 111 itself or within the electronics of the gyroscope system 100 due to the proximity of the primary drive transducer 112 to the primary pick-off transducer 113 and the secondary pick-off transducer 114. However, the Q of the structure 111 is affected by temperature. This means that the amplitude of the primary sense drive signal may change significantly with temperature as the Q of the structure 111 changes.

[0044] Coupling of the primary sense drive signal on the secondary sense pickoff transducer signal is particularly problematic because the primary sense drive signal may be indistinguishable from the signal caused by the angular rotation of vibratory gyroscope 110. This introduces pickoff bias errors in the output of vibratory gyroscope 110 that vary over temperature (because temperature changes change the Q of structure 111, and therefore the amplitude of the primary sense drive signal).

[0045] Coupling of the primary sense drive signal into the primary sense pickoff transducer signal is also a problem, but to a lesser extent this reduces the accuracy of detection of resonance of structure 111. However, because the amplitude of the primary sense pickoff transducer signal resulting from resonance of structure 111 is large, the effect is relatively small.

[0046] Gyroscope system 100 provides a means to measure the magnitude of such coupling for a given primary sense drive signal, and thus identify one or more pickoff bias errors, which is accomplished by operating vibratory gyroscope 111 in a diagnostic mode, as described below.

[0047] When vibratory gyroscope 110 is operating in a diagnostic mode, primary drive transducer 112 receives a large amplitude primary diagnostic drive signal at a frequency other than the resonant frequency of structure 111 (i.e., at a non-resonant frequency), which causes primary drive transducer 112 to drive structure 111 at the non-resonant frequency.

[0048] The non-resonant frequency should be removed from the resonant frequency of the structure 111 so that there is no significant resonant motion in the structure 111. In particular, the non-resonant frequency is selected so as not to induce vibration in the structure 111, i.e., the structure 111 does not vibrate in the diagnostic mode. This can be achieved, for example, by setting the difference between the non-resonant frequency and the resonant frequency of the structure 111 to be greater than 100 Hz.

[0049] Because structure 111 is driven at a non-resonant frequency, primary pickoff transducer 113 does not detect any vibration of structure 111. However, due to the coupling effects described above, primary pickoff transducer 113 still outputs a primary diagnostic pickoff transducer signal that is a measure of the magnitude of coupling in primary loop 123. This signal is received by primary loop 123 and provided to controller 160. Similarly, secondary pickoff transducer 114 does not detect any vibration of structure 111, but still outputs a secondary diagnostic pickoff transducer signal that is a measure of the magnitude of coupling in secondary loop 124. This signal is received by secondary loop 124 and provided to controller 160.

[0050] Controller 160 then compensates the primary and secondary sense drive signals when operating vibratory gyroscope 110 in the sense mode.

[0051] Specifically, controller 160 determines a ratio of the primary sense drive signal to the primary diagnostic drive signal obtained at any time during the sense mode and multiplies the secondary diagnostic pickoff transducer signal by this ratio to determine the secondary pickoff bias error. The secondary pickoff bias error is then subtracted from the secondary sense drive signal of secondary drive transducer 115 such that the secondary pickoff bias error is not nullified by secondary drive transducer 115. This prevents secondary drive transducer 115 from generating a bias offset, and thus the secondary pickoff bias error is removed from the output of vibratory gyroscope 110, providing a more accurate value of the rotational angular rate of vibratory gyroscope 110.

[0052] When the controller 160 operates the vibratory gyroscope 110 in the sensing mode, the controller 160 may similarly correct the primary sense drive signal of the primary drive transducer 112 by multiplying the primary diagnostic pickoff transducer signal acquired in the diagnostic mode by a ratio of the primary sense drive signal to the primary diagnostic drive signal to determine a primary pickoff bias error. The primary pickoff bias error is then subtracted from the primary sense drive signal of the primary drive transducer 112 so that the primary pickoff bias error is not nullified by the primary drive transducer 112. This prevents degradation of the amplitude or phase accuracy of the primary sense drive signal.

[0053] The amplitude of the primary diagnostic drive signal is fixed at a value that maximizes the amplitude of the primary and secondary diagnostic pickoff transducer signals to improve the sensitivity of the gyroscope system 100 .

[0054] The primary drive transducer 112 can drive the structure 111 at a non-resonant frequency above the resonant frequency of the structure 111 and / or at a non-resonant frequency below the resonant frequency of the structure 111. When the primary drive transducer 112 drives the structure 111 at non-resonant frequencies both above and below the resonant frequency of the structure 111, multiple pickoff bias errors can be identified in the sense mode for each of the primary loop 123 and the secondary loop 124. The frequency dependence on the coupling of the primary sense drive signal in the primary sense pickoff transducer signal and the secondary sense pickoff transducer signal can then be removed by averaging the multiple pickoff bias errors of the primary loop 123 and the secondary loop 124.

[0055] The controller 160 may be configured to switch the vibratory gyroscope 110 between a sensing mode and a diagnostic mode, or between a diagnostic mode and a sensing mode. However, it will be appreciated that this introduces some dead time into the gyroscope system 100 to allow the structure 111 to stop vibrating at its resonant frequency. This dead time can be reduced by actively damping the radial vibrations of the vibratory gyroscope 110, minimizing the delay when switching between the two operating modes.

[0056] In this case, the primary pick-off transducer 113 detects radial vibrations of the structure 111 and outputs a primary damped pick-off transducer signal to an amplitude control loop 118. This signal is amplified by a primary pick-off amplifier 117 and provided to a frequency control loop 119. A phase-locked loop 120 adjusts the phase of the amplified signal and a voltage-controlled oscillator 121 adjusts the frequency of the amplified signal to suppress the detected radial vibrations. The adjusted signal is then sent to a primary drive circuit 116 where the signal is amplified and then provided to the primary drive transducer 112 as a primary damped drive signal. The primary drive transducer 112 then drives the structure 111 to nullify the detected radial vibrations.

[0057] Additionally or alternatively, in a closed loop configuration, the secondary pick-off transducer 114 detects radial vibrations of the structure 111 and outputs a secondary damped pick-off transducer signal to the secondary loop 124. This signal is amplified by a secondary pick-off amplifier 125 and provided to a first demodulator 126 where the "real" component is extracted, and to a second demodulator 127 where the "quadrature" component is extracted. The "real" and "quadrature" components are recombined and sent to a secondary drive amplifier 128, which amplifies the signal and then provides the amplified signal to the secondary drive transducer 115 as a secondary damped drive signal 115. The secondary drive transducer 115 then drives the structure 111 to nullify the detected radial vibrations.

[0058] Once the structure 111 has ceased vibrating, the vibratory gyroscope 110 may be operated in the desired mode.

[0059] 2, the gyroscope system 100 may include an additional vibratory gyroscope 140. Similar to the vibratory gyroscope 110, the additional vibratory gyroscope 140 includes a structure 141, an amplitude control loop 148 and a frequency control loop 149 forming a primary loop 153, a phase-locked loop 150, a primary drive amplifier 146, an automatic gain control circuit 152, a primary drive transducer 142, a primary pick-off transducer 143, a primary pick-off amplifier 147, a voltage controlled oscillator 151, a secondary loop 154, a secondary pick-off transducer 144, a secondary pick-off amplifier 155, and a first demodulator 156. The additional vibratory gyroscope 140 may also include a secondary drive transducer 145, a second demodulator 157, and a secondary drive amplifier 158.

[0060] The operation of the additional vibratory gyroscope 140 when the additional vibratory gyroscope 140 operates in the sensing mode is the same as the operation of the vibratory gyroscope 110 when the vibratory gyroscope 110 operates in the sensing mode. Furthermore, the operation of the additional vibratory gyroscope 140 when the additional vibratory gyroscope 140 operates in the diagnostic mode is the same as the operation of the vibratory gyroscope 110 when the vibratory gyroscope 110 operates in the diagnostic mode. Furthermore, the operation of the additional vibratory gyroscope 140 when switching between the sensing mode and the diagnostic mode, or between the diagnostic mode and the sensing mode, is the same as the operation of the vibratory gyroscope 110 when switching between the sensing mode and the diagnostic mode, or between the diagnostic mode and the sensing mode. Therefore, a repeated description will be omitted.

[0061] The vibratory gyroscope 110 and the additional vibratory gyroscope 140 may operate in a sensing mode or a diagnostic mode simultaneously, however, in alternative embodiments, the vibratory gyroscope 110 and the additional vibratory gyroscope 140 operate in different modes.

[0062] 3, in a first step 201, the controller 160 operates the vibratory gyroscope 110 in a sensing mode and the additional vibratory gyroscope 140 in a diagnostic mode. Once the controller 160 identifies the primary and secondary pickoff bias errors of the additional vibratory gyroscope 140, in a second step 202, the controller 160 switches the additional vibratory gyroscope to operate in a sensing mode and corrects the primary and secondary sense drive signals of the additional vibratory gyroscope 140. Then, in a third step 203, the controller 160 switches the vibratory gyroscope 110 to operate in a diagnostic mode.

[0063] Once the controller 160 has identified the primary and secondary pickoff bias errors of the vibratory gyroscope 110, in a fourth step 204, the controller 160 switches the vibratory gyroscope 110 to operate in a sense mode and corrects the primary and secondary sense drive signals of the vibratory gyroscope 110. Then, in a fifth step 205, the controller 160 switches the additional vibratory gyroscope 140 to operate in a diagnostic mode.

[0064] Thus, the controller 160 may be configured to continuously cycle through the vibratory gyroscopes 110, 140, with each vibratory gyroscope 110, 140 operated in a diagnostic mode at least once while the other vibratory gyroscope 110, 140 is operating in a sensing mode, allowing the gyroscope system 100 to compensate for the outputs of the vibratory gyroscopes 110, 140 while the gyroscope system 100 is operating.

[0065] When the vibratory gyroscope 110 is operating in the sensing mode, the additional vibratory gyroscope 140 may operate in the same configuration as the additional vibratory gyroscope 140 when operating in the sensing mode, i.e., in a closed-loop configuration or an open-loop configuration. Alternatively, the vibratory gyroscope 110 may operate in a closed-loop configuration when operating in the sensing mode and the additional vibratory gyroscope 140 may operate in an open-loop configuration when operating in the sensing mode, or vice versa.

[0066] 4, in some embodiments, the vibratory gyroscope 110 may include a pair of primary drive transducers 112, a pair of primary pick-off transducers 113, and a pair of secondary pick transducers 114. The vibratory gyroscope 110 may also include a pair of secondary drive transducers 115. Each pair may be positioned opposite each other around the circumference of the vibratory gyroscope 110. However, this is not required, i.e., each pair may be positioned at any position relative to each other. The additional vibratory gyroscope 140 may be identical to the vibratory gyroscope 110.

[0067] 5, in some embodiments, the gyroscope system 100 includes at least four vibratory gyroscopes 110, 140, 150, 170 arranged in a tetrahedral shape, where the controller 160 operates at least one of the vibratory gyroscopes 110, 140, 150, 170 in a diagnostic mode while one or more of the other vibratory gyroscopes 110, 140, 150, 170 operates in a sensing mode.

[0068] As is well known by those skilled in the art, when these vibratory gyroscopes are operated in a sensing mode, the tetrahedral arrangement allows the rotational angular rate of the gyroscope system 100 to be determined about all three principal axes (x, y, and z) by mathematically transforming the outputs of any three of the four vibratory gyroscopes 110, 140, 150, 170. The rotational angular rate of the gyroscope system 100 can be determined while the fourth vibratory gyroscope is operating in a diagnostic mode. Unlike some other diagnostic tests, since the diagnostic mode is performed without vibrating the structure 111 while it is not resonating, i.e., the pickoff bias error is not affected by the angular rotation of the gyroscope system 100, there is no need to correct for the pickoff bias error due to the effect of the angular rotation of the gyroscope system 100 about the axis of the fourth vibratory gyroscope.

[0069] Various aspects of the gyroscope system disclosed in the various embodiments may be used alone, in combination, or in various arrangements not specifically described in the above embodiments, and therefore the present disclosure is not limited in its application to the details and arrangements of components set forth in the above description or drawings. For example, aspects described in one embodiment may be combined in any manner with aspects described in other embodiments. Although specific embodiments have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects. The scope of the following claims should not be limited by the embodiments shown in the examples, but should be accorded the broadest reasonable interpretation consistent with the description as a whole.

Claims

1. at least one vibratory gyroscope having a structure, one or more drive transducers configured to drive the structure, and one or more pick-off transducers configured to detect vibrations of the structure, the vibratory gyroscope configured to operate in a sensing mode or a diagnostic mode, the vibratory gyroscope configured to measure a rotational angular rate of the vibratory gyroscope during the sensing mode; a controller configured to operate the vibratory gyroscope in the diagnostic mode such that the one or more drive transducers drive the structure at a frequency other than a resonant frequency of the structure; A gyroscope system comprising:

2. The gyroscope system of claim 1 , wherein the controller is configured to operate the vibratory gyroscope in the diagnostic mode to identify one or more pickoff bias errors of the vibratory gyroscope.

3. 3. The gyroscope system of claim 2, wherein the controller is configured to receive one or more diagnostic pickoff transducer signals from the vibratory gyroscope when operating the vibratory gyroscope in the diagnostic mode, and the controller is configured to identify the one or more pickoff bias errors of the vibratory gyroscope based on the one or more diagnostic pickoff transducer signals.

4. 4. The gyroscope system of claim 2, wherein the controller is configured to correct an output of the vibratory gyroscope based on the one or more pickoff bias errors of the vibratory gyroscope when the controller operates the vibratory gyroscope in the sensing mode.

5. 5. The gyroscope system of claim 4, wherein the control is configured to receive one or more sensing pickoff transducer signals from the vibrating gyroscope when operating the vibrating gyroscope in the sensing mode, and the controller is configured to correct the output of the vibrating gyroscope by subtracting the one or more pickoff bias errors of the vibrating gyroscope from the one or more sensing pickoff transducer signals when operating the vibrating gyroscope in the sensing mode.

6. 10. The gyroscope system of any preceding claim, wherein the one or more drive transducers are configured to drive the structure such that substantially no vibration of the structure occurs when operating the vibratory gyroscope in the diagnostic mode.

7. 10. The gyroscope system of any preceding claim, wherein the controller is configured to switch the vibratory gyroscope from operation in the diagnostic mode to operation in the sensing mode or from operation in the sensing mode to operation in the diagnostic mode, and the controller is configured to suppress vibrations of the structure when the vibratory gyroscope is switched from operation in the sensing mode to operation in the diagnostic mode.

8. 10. The gyroscope system of any preceding claim, wherein the one or more drive transducers include one or more primary and / or secondary drive transducers, and the one or more pick-off transducers include one or more primary and / or secondary pick-off transducers.

9. 10. A gyroscope system according to any preceding claim, comprising an additional vibratory gyroscope having a structure, one or more drive transducers configured to drive the structure, and one or more pick-off transducers configured to detect vibrations of the structure, the additional vibratory gyroscope configured to operate in a sensing mode or a diagnostic mode, the additional vibratory gyroscope configured to measure a rotational angular rate of the vibratory gyroscope during the sensing mode.

10. 10. The gyroscope system of claim 9, wherein the controller is configured to operate one of the vibratory gyroscopes in the diagnostic mode while the other vibratory gyroscope operates in the sensing mode.

11. 11. The gyroscope system of claim 10, wherein the controller is configured to cycle through the vibratory gyroscopes such that each vibratory gyroscope is operated in the diagnostic mode at least once while the other vibratory gyroscope is operating in the sensing mode.

12. 11. A gyroscope system according to any preceding claim, comprising a total of four vibratory gyroscopes, each vibratory gyroscope having a structure, one or more drive transducers configured to drive the structure, and one or more pick-off transducers configured to detect vibrations of the structure, each vibratory gyroscope configured to operate in a sensing mode or a diagnostic mode, and each vibratory gyroscope configured to measure a rotational angular rate of the vibratory gyroscope during the sensing mode.

13. The gyroscope system of claim 12 , wherein the vibratory gyroscopes are arranged in a tetrahedral shape.

14. An inertial measurement unit comprising a gyroscope system according to any preceding claim.

15. 1. A method of operating an angular rate sensor including at least one vibratory gyroscope having a structure, one or more drive transducers configured to drive the structure, and one or more pick-off transducers configured to detect vibrations of the structure, the vibratory gyroscope configured to operate in a sensing mode or a diagnostic mode, the vibratory gyroscope configured to measure a rotational angular rate of the vibratory gyroscope during the sensing mode, the method comprising: operating the vibratory gyroscope in the diagnostic mode such that the one or more drive transducers drive the structure at a frequency other than a resonant frequency of the structure. How an angular rate sensor works.

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