Vibratory structure gyroscope, operating method of vibratory structure gyroscope, and calibration method of gyroscope

Abstract

To provide an improved vibration structure gyroscope and its operation method.SOLUTION: A vibration structure gyroscope (30) includes a resonance structure (10) composed so as to be vibrated by receiving stimuli from a primary drive electrode. A drive system is configured so as to vibrate the vibration structure at a resonance frequency. An automatic gain control device (34) changes the amplitude of a primary drive signal (PD). A controller (44) operates the gyroscope (30) such that the automatic gain control device (34) changes the amplitude of the drive signal (PD) in an operation range defined by an upper limit and a lower limit in a first operation mode. The controller (44) can also operate the gyroscope (30) in a second operation mode, and the automatic gain control device (34) sets the amplitude of the control signal (PD) to a predetermined level outside the operation range in the second operation mode.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to vibrating structure gyroscopes, in particular to microelectromechanical system (MEMS)-based vibrating structure gyroscopes for measuring angular velocity(ies), e.g., within an inertial measurement unit (IMU). The present disclosure relates to inductive gyroscopes in particular, although not limited thereto.

Background Art

[0002] A gyroscope is a sensor that measures angular velocity (i.e., rotational speed). Gyroscopes are used in many applications including inertial navigation, robotics, avionics, and automobiles. In inertial navigation applications, gyroscopes can be mounted in a self-contained system called an “inertial measurement unit” (IMU). An IMU typically includes multiple accelerometers and / or gyroscopes and provides estimates of an object's motion parameters such as angular velocity, acceleration, attitude, position, and velocity based on the outputs of the gyroscope(s) and / or accelerometer(s).

[0003] MEMS-based gyroscopes have become widely popular in recent years and are often much more effective than their conventional macro counterparts. MEMS-based gyroscopes are typically implemented using a vibrating structure and are often referred to in the art as “vibrating structure gyroscopes” or “VSGs”. A vibrating structure gyroscope generally includes a mass body that has been micromachined and is configured to vibrate. Representative examples of vibrating structure gyroscopes include vibrating ring gyroscopes and vibrating tuning fork gyroscopes, and there are also vibrating structures including, for example, beams, cylinders, hemispherical shells, and disks.

[0004] In normal operation, a mass body subjected to micromachining is driven to vibrate in a pre-specified vibration mode, typically in a cos nθ vibration mode (e.g., n = 2). This driven vibration mode is usually referred to as the primary mode. When the gyroscope rotates, a Coriolis force acts on the vibrating mass body, and this force can cause the mass body to vibrate in a secondary vibration mode different from the primary mode. Generally, the secondary vibration mode occurs in addition to the primary mode, and in the secondary mode, the mass body vibrates along a direction different from the vibration of the pre-specified primary mode.

[0005] Since the amplitude of the vibration in the secondary mode is proportional to the rotation speed, by using an appropriate sensor (e.g., an inductive or capacitive transducer) to directly detect the amplitude of the secondary vibration, the angular velocity (e.g., measured in degrees per second) can be obtained (this is called "open-loop measurement"). Alternatively, the angular velocity can also be measured by canceling the vibration in the secondary mode and applying a restoring force so that the mass body continues to vibrate only in the primary mode. The restoring force is usually based on the detected amplitude of the secondary vibration. Since the restoring force is proportional to the applied angular velocity, the amplitude of the signal required to disable the secondary mode provides a measure of the angular velocity. This latter configuration is known in the art as "closed-loop measurement". For example, in US5,419,194 and US8,347,718, examples of methods for measuring angular velocity are described.

[0006] A problem with vibrating structure gyroscopes is that it is difficult to determine the "quality factor" (often called the "Q factor" or simply "Q") of a resonator (e.g., a silicon ring) once it is incorporated into the gyroscope. This difficulty is caused by the interaction with the electronic equipment that supports both driving and pick-off, which is necessary to enable the resonator to be used as a gyroscope. When using the resonator as a gyroscope, it is also difficult to distinguish the various signals required for velocity measurement or Q measurement.

[0007] One skilled in the art will understand that the Q of a gyroscope is a measure of the quality of resonance achieved by a resonator. That is, a high Q means relatively little attenuation and that the resonator vibrates at a relatively high amplitude at the resonance frequency for a relatively long time, while a low Q means relatively more attenuation and thus the vibration decays and disappears more quickly. Generally, a gyroscope preferably has a high Q.

[0008] If the Q of a gyroscope can be determined, it can be beneficial for several reasons. One such reason is that a gyroscope can generally suffer from a "scale factor error" that must be resolved by an error compensation process. The "scale factor error" in a gyroscope is an error in which the angular velocity detected by the gyroscope is underestimated or overestimated by a certain percentage compared to the actual angular velocity, and a percentage value is used. For example, a scale factor error of 0.1% at an angular velocity of 60° / s results in an absolute error of 0.06° / s. To compensate for such a scale factor error, usually, an adjustment is made to the primary drive signal applied to the gyroscope to cancel out the scale factor error.

[0009] In some gyroscopes, for example, induction gyroscopes, permanent magnets are utilized and the resonant structure is arranged in the B - field of the permanent magnet exclusively in a manner known in the art. When the strength of the B - field decreases, generally, it results in an increase in the primary drive level required to correct the resulting change in the scale factor.

[0010] Generally, the primary drive level for a given amplitude is determined by both the magnetic field strength and the Q of the resonator. However, since the magnetic field strength is directly related to the scale factor while Q is not, for the B-field scale factor correction to function, variations in Q must be accounted for either by characterization or measurement. One skilled in the art will understand that the Q of a resonator generally varies significantly with temperature, but may also vary over the life of the device. Summary of the Invention Problems to be Solved by the Invention

[0011] Accordingly, the present invention provides an improved vibrating structure gyroscope and a method of operating the same. Means for Solving the Problems

[0012] According to the present disclosure, a vibrating structure gyroscope comprising: a resonant structure configured to vibrate in response to stimulation from a primary drive electrode; a drive system configured to vibrate the vibrating structure at a resonant frequency, the drive system comprising a primary drive electrode configured to induce motion in the vibrating structure and a primary sense electrode configured to sense motion of the vibrating structure; an automatic gain control device configured to vary the amplitude of a drive signal applied to the primary drive electrode; a controller configured to operate the gyroscope, the controller: in a first operating mode, causing the automatic gain control device to vary the amplitude of the drive signal between an operating range defined by a lower limit and an upper limit; and in a second operating mode, causing the automatic gain control device to set the amplitude of the drive signal to a predetermined level outside the range of the operating range; and comprising a controller configured to operate the gyroscope to perform the above. When the gyroscope is operating in the second operating mode, the controller: Measuring the amplitude of the sense signal from the primary sense electrode after the elapse of a predetermined period, Determining the number of vibration cycles during a predetermined period, and Determining the quality factor of the gyroscope from the measured amplitude and the number of vibration cycles, is performed. A vibrating structure gyroscope is provided.

[0013] The first aspect of the present disclosure also extends to an inertial measurement unit (IMU) including the above-described vibrating structure gyroscope. The first aspect of the present disclosure further extends to an electronic device including the above-described vibrating structure gyroscope.

[0014] The first aspect of the present disclosure extends to a method of operating a vibrating structure gyroscope and to a vibrating structure gyroscope including A resonant structure configured to vibrate in response to a stimulus from a primary drive electrode, and A drive system configured to vibrate the vibrating structure at a resonant frequency, the drive system including a primary drive electrode configured to induce motion in the vibrating structure and a primary sense electrode configured to sense the motion of the vibrating structure, An automatic gain control device configured to change the amplitude of a drive signal applied to the primary drive electrode, and The method includes Operating the gyroscope In a first operation mode, the automatic gain control device changes the amplitude of the drive signal between an operating range defined by a lower limit and an upper limit, and In a second operation mode, the automatic gain control device sets the amplitude of the drive signal to a predetermined level outside the range of the operating range, and operating so as to perform When operating the gyroscope in the second operation mode, the method further includes Measuring the amplitude of the sense signal from the primary sense electrode after the elapse of a predetermined period, Determining the number of vibration cycles during a predetermined period, and Determining the quality factor of the gyroscope from the measured amplitude and the number of vibration cycles.

[0015] The first aspect of the present disclosure also extends to a non-transitory computer-readable medium including instructions that, when executed by a processor, cause the processor to execute a method of operating the above-described vibrating structure gyroscope. The first aspect of the present disclosure also further extends to a computer software product including instructions that, when executed by a processor, cause the processor to execute a method of operating the above-described vibrating structure gyroscope.

[0016] Thus, it will be appreciated that embodiments of the present disclosure provide an improved gyroscope and method of operating the same in which an automatic gain control (AGC) device is “overridden” to apply a fixed amplitude to one or more primary drive electrodes. Thereby, the resonant structure resonates and the resulting resonance is measured using sense electrodes. It should be understood that the signal applied to the drive electrode(s) is often referred to as the “drive signal” and the signal obtained from the sense electrode(s) is often referred to as the “pickoff signal” or “sense signal”. More specifically, these signals are respectively a “primary drive signal” and a “primary pickoff / sense signal”.

[0017] In test mode, the AGC sets the amplitude (i.e., “level”) of the primary drive signal to a fixed value outside the range of the normal operating range. The predetermined amplitude set for the drive signal in the second mode may be higher than the upper limit, but in a set of preferred embodiments, the predetermined level set for the amplitude in the second mode is less than the lower limit. In such a set of embodiments, this “test amplitude” may be zero.

[0018] A further advantage of the configuration of the present disclosure is that the required gyroscope Q can be used as an indicator of the overall "health" of the gyroscope. A change in the gyroscope Q can be used, for example, as an early indication of physical degradation of the gyroscope, which may indicate that maintenance or replacement of the device is necessary. Thus, since the primary drive can be adjusted to compensate for changes in Q, the gyroscope can continue to function properly, while in the present disclosure, this change in Q can be detected early so that preventive measures can be taken, for example, before device failure.

[0019] The resonant structure may include a substantially planar ring structure in at least some embodiments. In one set of embodiments where overlap is possible, the resonant structure is made of silicon.

[0020] The present disclosure can be applied to, for example, inductive gyroscopes, capacitive gyroscopes, and piezoelectric gyroscopes. However, the principles of the present disclosure have been found to be particularly advantageous when applied to inductive gyroscopes. Thus, in at least some embodiments, the gyroscope is an inductive gyroscope. In some such embodiments, the gyroscope includes a permanent magnet and the resonant structure is disposed within the magnetic field of the permanent magnet.

[0021] Generally, in an inductive gyroscope, scale factor errors can occur due to fluctuations in the magnetic field (i.e., the B-field) of the magnet used in the inductive gyroscope. These fluctuations can be compensated for, for example, solely using first-order drive compensation techniques known in the art, and it has been found that this first-order drive is sensitive to fluctuations in both the Q of the gyroscope and the B-field. The applicant understands that the principles of the present disclosure have the effect of being able to separate these contributions, better compensate for fluctuations in the scale factor, thereby reducing scale factor errors and improving the overall accuracy of the inductive gyroscope, and that the fluctuations in Q can be considered when determining how to vary the first-order drive.

[0022] Specifically, when the magnet deteriorates (e.g., naturally over time as the material ages), the magnetic field weakens. As a result, the amplitude of the motion induced in the vibration structure decreases, and the amplitude of the pickoff signal detected by the first-order sense electrode decreases. In some embodiments, the gyroscope is configured to determine a deterioration coefficient of the magnet. As a non-limiting example, a suitable method for determining magnet deterioration is described in US2020 / 0200536, the content of which is incorporated herein by reference.

[0023] To compensate for fluctuations in the amplitude (e.g., due to fluctuations in Q and, at least in the case of an inductive gyroscope, potentially the magnet deterioration coefficient corresponding to weakening of the magnet's B-field), the AGC device automatically increases the gain. Thus, the gain of the drive control loop can be used as a measure of magnet deterioration and can be used to compensate for changes in the scale factor caused by that magnet deterioration. By comparing the gain of the drive control loop during use with a reference value of the gain of the drive control loop obtained during calibration, the change in the scale factor after calibration can be calculated using the change in gain from the reference value.

[0024] The gyroscope of the present disclosure can "cancel out" the change in the primary drive of the induced gyroscope caused by the variation of Q because it independently obtains the Q of the gyroscope, and can attribute the remaining change in the primary drive to the deterioration of the magnet, enabling compensation for this magnet deterioration. Thus, by this process, the scale factor of the gyroscope can be accurately compensated throughout its lifespan as the magnet deteriorates over time. Most changes in the magnetic field strength of the magnet are expected to be due to the process of aging, but note that the magnetic field strength can also be affected by other factors such as exposure to an external magnetic field environment, severe shock, or other damage. Changes that weaken the magnet will also result in a corresponding increase in the gain in the drive control loop and will be appropriately compensated by this system regardless of any variation in Q.

[0025] The test procedure facilitated by the present disclosure can be implemented by switching the gyroscope to a second mode. This may be done at startup (i.e., when power is applied to the gyroscope), but additionally or alternatively, during normal operation of the gyroscope, the gyroscope may be intermittently, e.g., periodically, switched from a first mode to a second mode over a predetermined period and then switched back to the first mode.

[0026] In some such embodiments, the controller is configured to alternately operate the gyroscope between a first mode and a second mode. In such a set of embodiments, the controller performs this alternating repetition according to a specific duty cycle. In other words, the gyroscope operates for X% of the time in a first mode (i.e., the "normal" mode) and for (100 - X)% of the time in a second mode (i.e., the "Q measurement" mode). The duty cycle (i.e., the value of X) can be selected as needed so that the normal operation of the gyroscope can continue reliably without being substantially hindered, that is, even if a certain percentage of the operating time is spent on the measurement of Q, the measurement of the angular velocity can still be carried out continuously.

[0027] The derivation of the Q factor may be performed in a single derivation step in some embodiments, but in some embodiments, the controller is configured to determine the Q factor over multiple operations of the AGC device in the second mode. In at least some such embodiments, the controller may apply a filter such as a low-pass filter to successively determine multiple Q factors. In this way, a better estimated value of Q can be obtained by averaging (or "smoothing") several measured values of Q.

[0028] The present disclosure can be applied to both open-loop and closed-loop gyroscope systems. In an open-loop system, the signal(s) obtained from the sense electrode(s) is used as a measure of the angular velocity. In a closed-loop system, the gyroscope may further include a drive control loop that controls the primary drive electrode according to the primary sense electrode.

[0029] The drive system of the oscillatory structure gyroscope may include a feedback loop (or "drive control loop") that includes an AGC device that attempts to maintain the correct amplitude of the resonant motion of the gyroscope's oscillatory structure over the product's useful life and over different temperatures and different operating conditions. The primary sense electrode (also called the primary pickoff electrode) generates a signal from the motion of the oscillatory structure. To provide the necessary feedback, the drive control loop must measure the signal from the primary sense electrode and apply a proportional signal to the primary drive electrode. The amount of gain required for this amplification will be adjusted by the AGC so as to achieve and maintain the desired amplitude of the resonant motion. Thus, the AGC device preferably adjusts the gain to maintain a stable resonance. The drive control loop also includes, in at least some embodiments, a phase-locked loop (PLL) configured to maintain the phase and frequency of the drive signal provided to the primary drive electrode at the same phase and frequency as the resonant frequency of the resonant structure.

[0030] The gain of the drive control loop can be measured in several different ways, all of which are known in the art. For example, the loop gain coefficient can be derived from the AGC or the like. This can be measured or output as an analog signal or a digital value. Thus, in one set of embodiments where the gyroscope is an inductive gyroscope, a signal representing the gain of the drive control loop can then be used as an indicator of the amount of magnet degradation and, thus, can be used (either directly or indirectly) to generate a magnet degradation coefficient.

[0031] In some embodiments, the gyroscope further comprises a compensation device configured to receive a requested Q factor and output a scale factor correction based on the requested Q factor. In such a particular set of embodiments, the scale factor correction can be based on the requested Q factor and the drive signal applied to the primary drive electrode (i.e., the primary drive signal).

[0032] In a set of embodiments where the gyroscope is an inductive gyroscope and a degradation factor of a magnet is determined, the degradation factor of the magnet may be used by a compensation device when generating a scale factor correction, or may be used to generate an additional scale factor correction based on the degradation factor of the magnet.

[0033] Generally, temperature can affect the operation of a gyroscope. The scale factor as well as gains, drive signals, and / or pickoff signals can also vary with temperature. Accordingly, the compensation device may be configured to receive a temperature-dependent signal (e.g., from a temperature sensor) and output a scale factor correction based on both the signal from the drive system and the temperature-dependent signal. To that end, the compensation device may include a suitable compensation mechanism configured to provide a scale factor correction value in response to both the determined Q factor and the temperature-dependent signal (and optionally, a scale factor correction for the B field if necessary). In some embodiments, the compensation mechanism includes a look-up table or a polynomial. The temperature-dependent signal may be provided by a temperature sensor, but in some embodiments, the temperature-dependent signal is extracted as a temperature-dependent component of another signal generated by the gyroscope.

[0034] The gyroscope may further include a sensing system configured to sense vibrations of a vibrating structure and output an angular velocity signal based on the sensed vibrations, and this vibrating structure gyroscope is configured to apply a scale factor correction to the angular velocity signal to provide an output of this vibrating structure gyroscope. The sensing system is used to detect a second-order vibration mode (which, in a vibrating ring gyroscope, is typically at an angle of 45 degrees with respect to the first-order (drive) vibration mode when the gyroscope is operating in the cos 2θ mode), and the amplitude thereof is related to the rotational speed of the gyroscope.

[0035] According to another aspect of the present disclosure, a method of calibrating a gyroscope, Providing the gyroscope described above, Determining the Q factor of the gyroscope during the startup process and / or during normal operation of the gyroscope, Based on the obtained Q factor, storing information that enables quantification of scale factor correction from the Q factor, a method is provided.

[0036] This information can be stored in a compensation device (if provided) or in a memory. The step of determining the Q factor may include determining the Q factor over a temperature range. The storing step may include storing the information in a look-up table.

[0037] Next, as non-limiting examples, one or more non-limiting embodiments will be described with reference to the accompanying drawings.

Brief Description of the Drawings

[0038]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0039] Referring to FIG. 1, a vibration structure type ring gyroscope 1 by an induction method is shown. A ring-shaped resonator 10 (i.e., a resonance structure) is attached to a support frame 12 by flexible support legs (not shown). These support legs extend from the outer periphery of the resonator 10 to the support frame 12, enabling the resonator 10 to vibrate in the primary vibration mode and the secondary vibration mode. The support frame 12 is attached to a glass pedestal 14, and the glass pedestal 14 is attached on a glass substrate 16.

[0040] The magnet assembly 18 includes a lower pole piece 20, an upper pole piece 24, and a permanent magnet 22 installed (or "sandwiched") between the lower pole piece 20 and the upper pole piece 24. The lower pole piece is attached to the substrate 16 under the resonator 10, and the upper pole piece 24 is formed as a cap, and the edge of the cap is formed above the resonator 10. The magnetic field generated by the permanent magnet 22 is directed into the resonator 10.

[0041] The vibrating ring 10 is installed between the upper pole piece 24 and the lower pole piece 20 so as to be placed in the magnetic field formed between these two pole pieces. The vibrating ring 10 is attached via external attachment legs (not shown) extending from the radially outer end of the ring 10 to the support frame 12 so that it can vibrate as described above. The support frame 12 is generally attached to the glass pedestal 14, and the glass pedestal 14 is generally attached on the glass substrate 16.

[0042] In use, magnetic flux lines pass through the gyroscope structure (i.e., ring 10). Conductive tracks are formed on the gyroscope structure (usually making a loop in a local part of the ring structure after passing through one of the mounting legs and then returning along the same or a different mounting leg). An AC current passes through these conductive tracks on the gyroscope structure, thereby creating a corresponding alternating magnetic field. Due to the attractive and repulsive forces between this alternating magnetic field and the permanent magnet, vibration is induced in the gyroscope structure. In a typical configuration, eight such loops are paired into four pairs (with diametrically opposed loops paired). These pairs are used to drive the primary vibration mode, sense (i.e., "pick off") the primary vibration mode, sense the secondary vibration mode, and (in the case of closed-loop operation) drive the ring structure to invalidate the secondary vibration mode.

[0043] The scale factor of gyroscope 1 is determined by the strength of the magnetic field (or "B-field") of magnet 22. Variations in the scale factor can be compensated for using primary drive. However, the primary drive of gyroscope 1 is affected by both the Q-factor (or "Q") of gyroscope 1 and the strength of the B-field of magnet 22. In order to be able to appropriately compensate the scale factor for changes in the B-field using primary drive, Q needs to be known.

[0044] The primary drive level for a given amplitude is determined by both the magnetic field strength of the resonator and Q. When the magnetic field strength of the permanent magnet (i.e., the B-field) decreases, it generally results in an increase in the primary drive level required to correct the resulting change in the scale factor.

[0045] However, while the B-field is directly related to the scale factor, Q is not. Therefore, for the B-field scale factor correction to function, variations in Q must be accounted for either by characterization or measurement.

[0046] Regarding the Q of gyroscope 1, this can vary both in the short term and the long term. Short-term factors that can affect Q include the temperature of the device, while long-term factors include the aging degradation of the device. This change in Q can have a significant adverse impact on the performance of gyroscope 1.

[0047] As magnet 22 ages, its magnetic field strength also generally tends to gradually decay over time. Thereby, the scale factor error of gyroscope 1 gradually increases. The change in the magnetic field strength of magnet 22 is small in the short term (generally between 100 ppm and 1000 ppm per year even under rather harsh operating conditions such as high temperature), but this change accumulates over time and can contribute significantly to the scale factor. For example, some gyroscopes are designed to have a service life of 20 years. During such a time scale, due to the change in the magnetic field strength of the magnet, a scale factor change of up to approximately 4% can occur (when the magnetic field strength changes by 2%, due to the combined effect on the secondary drive and the primary pickoff, the scale factor will change by 4%). In the case of high-precision and high-sensitivity gyroscopes, this change in the scale factor can have a significant impact, and generally, it is desirable to reduce this change by adjusting the primary drive controlled by the feedback loop.

[0048] In order to use the primary drive as a measure of the degradation of the magnet, it is important to know to what extent the change in the primary drive is due to the Q of gyroscope 1 and be able to separate these from the changes due to the degradation of the magnet.

[0049] Figure 2 shows the vibrating structure gyroscope 30 by the induction method together with its control and detection system. The physical structures of the resonator 10 and the magnet assembly 18 of gyroscope 30 may be the same as those shown in Figure 1.

[0050] The drive system 31 applies a drive signal P to the primary drive electrodes (which can actually be a pair of electrodes facing each other along the diameter)D is configured to provide. The primary pick-off electrode (primary sense electrode) located 90 degrees from the drive electrode around the resonator ring 10 generates a pick-off signal P P . The pick-off signal P P is amplified by the amplifier 32 and provided to a voltage controlled oscillator (VCO) and a phase locked loop (PLL) circuit 33, which adjusts the phase and frequency of the signal to lock to the resonance frequency of the resonator 10 to maintain the primary vibration mode. The adjusted primary drive signal P D is provided to the primary drive electrode through the amplifier 35 to maintain resonance. The pick-off signal P P is also provided in parallel to an automatic gain control (AGC) circuit 34 that adjusts the gain of the amplifier 35 so that the amplitude of the resonance is reliably maintained.

[0051] The operation of the AGC 34 is controlled by a controller 44. This controller 44 may be an individual hardware device, or may also be executed by software or firmware operating on a suitable processor (which may be specialized for this purpose or, if necessary, may execute one or more other functions related to the operation of the gyroscope). Specifically, the controller 44 operates to switch the AGC 34 between a first "normal" operating mode and a second "Q measurement" operating mode.

[0052] In its first, i.e., "normal", operating mode, the AGC 34 receives the primary pick-off signal P P amplified by the amplifier 32 and compares it with a threshold value. If the magnitude of the pick-off signal P P is smaller than the threshold value, the AGC 34 increases the gain of the amplifier 35, while if the magnitude of the pick-off signal P P is larger than the threshold value, the AGC 34 decreases the gain of the amplifier 35. Thereby, the magnitude of the primary drive signal P D changes, so that the amplitude of the vibration of the resonator changes, and thus the pick-off signal P PThe amplitude changes. In this way, the primary drive control loop (including amplifier 32, VCO / PLL 33, AGC 34, and amplifier 35) always adjusts the signal so as to resonate the resonator 10 and maintain it in a proper amplitude motion.

[0053] Amplifier 32 measures the amplitude of the primary pick-off signal P P (specifically, the "real" component of the signal), and this amplitude is used for generating a speed scale to compensate for the change in the primary amplitude due to the change in the AGC set level in both the "normal" and "Q measurement" modes. The output of amplifier 32 is provided to a sampling point 39 that generates a speed output as outlined below.

[0054] This speed signal is obtained via the secondary pick-off signal S P from the secondary pick-off electrode and amplifier 40.

[0055] The output S P from the secondary pick-off contains both the "real" and "quadrature" components in the observed signal, these components are in quadrature phase and are obtained by the frequency input from the primary loop. The "real" component provides the desired gyroscope output of the applied actual speed. The "quadrature" component is generated through the imperfection of the system that couples energy to the secondary motion, and this quadrature (i.e., 90°) component does not contribute to the speed output.

[0056] In an open-loop embodiment, the output of amplifier 40 is passed through a demodulator 42 to extract the real component, which is used as the speed output. In a closed-loop embodiment as shown in Figure 2, the output of amplifier 40 is also passed through a demodulator 43 to extract the quadrature component. The real component and the quadrature component are recombined and used to generate the secondary drive signal S D via amplifier 41, and this secondary drive signal S DIt is applied to the secondary drive electrodes to invalidate the motion of the second mode of the resonator 10. And the magnitude of the real part of the signal required to invalidate this motion is used as the velocity output (which may be corrected by the scale factor correction 37' at 39, as will be described in more detail below).

[0057] The gain of the AGC 34 is also provided as an output to a compensation device 36 that implements a compensation mechanism 38, which may be, for example, a look-up table, a polynomial, or any other suitable compensation mechanism. The compensation device 36 outputs a scale factor correction 37 based on the Q required by the controller 44 and supplies the scale factor correction 37 to the AGC 34, as will be outlined below.

[0058] The compensation device 36 (and the associated compensation mechanism 38) may actually be a function of the controller 44, that is, it will be understood that a single hardware device (e.g., a processor, a microcontroller, or the like) may perform the roles of both the controller 44 and the compensation device 36. Of course, depending on the design of the system, these may be separate devices instead. However, for ease of explanation and reference, these are shown as separate functional blocks in FIG. 2.

[0059] In the second operating mode, i.e., the "Q measurement" mode, the output of the AGC 34 is overridden such that the AGC 34 sets the level of the primary drive signal P D to a predetermined (i.e., fixed) level outside the range of magnitudes used during the first mode. The steps performed in this second operating mode will be outlined in more detail below.

[0060] It will be appreciated that the AGC 34 can also compensate for other operating conditions such as temperature changes. For example, the compensating device 36 may have a temperature-dependent input, and in this particular embodiment, this input is obtained from the temperature sensor 50, but may also be extracted from another signal having a temperature-dependent component. In such an embodiment, the compensating device 36 takes the temperature into account. For example, the compensating mechanism 38 can provide a temperature-dependent scale factor correction. If the compensating mechanism 38 is a look-up table, this look-up table can have entries for several different gain levels, for example, and for each gain level, can provide a scale factor compensation output for each of a plurality of temperatures.

[0061] According to the present system, the scale factor of the gyroscope 30 can be corrected throughout the product life while the magnet 22 is subject to aging and / or performance degradation, regardless of the change in Q. When Q is determined by the controller 44, appropriate changes can be made to the primary drive signal P D to compensate for the change in the scale factor due to the deterioration of the magnet.

[0062] The magnitude of Q determined by the controller 44 can also be used for the health monitoring of the gyroscope 30. Specifically, the controller 44 may output a health index signal 45 that provides information regarding the overall health of the gyroscope 30. This index signal 45 may be an alarm signal (i.e., a flag) generated when Q deteriorates beyond a threshold, and / or may convey a suitable metric (e.g., a metric derived from Q) that indicates the health according to a specific scale. In some configurations, the health index signal 45 may be the determined Q value itself. The state of the index signal 45 can be used, for example, to determine whether maintenance or replacement of the gyroscope 30 is necessary.

[0063] As outlined above, when the controller 44 operates the gyroscope 30 in the second operating mode, i.e., the "Q measurement" operating mode, the AGC 34 sets the level of the primary drive signal P D to a predetermined fixed value. The controller 44 alternately switches the operation between the first mode and the second mode according to a specific duty cycle. In some embodiments, the controller may switch the gyroscope 30 to the second mode for a predetermined period of 0.5 to 1.0 seconds, and after the elapse of the predetermined period, the vibration amplitude may be measured using the primary pick-off electrode(s). Of course, it will be understood that different periods may be used as necessary. At the end of this predetermined period, the controller 44 switches the gyroscope 30 back to the first (i.e., normal) operating mode, at which point the AGC 34 resumes controlling the gain as outlined previously.

[0064] By extending the operation in the second mode, it becomes possible to measure Q more accurately. However, if the operation outside the range of the first mode is too long, excessive attenuation may occur, which has been found to affect the measurement of the angular velocity performed in the first mode. Therefore, generally, the controller 44 may average the Q measurement values over time, and the duty cycle may be selected such that normal operation can continue without substantial interference. The specific duty cycle that enables this movement may depend, for example, on the device actually used, as well as its material and structural characteristics.

[0065] As shown in FIG. 2, the controller 44 is connected to the AGC 34 and can issue a command to set the output of the AGC 34 to a desired level. This may be an analog control signal or a digital control signal as necessary. The level of the AGC 34 is set to a value outside the normal operating range (i.e., outside the range of values defined by the upper and lower limits used in the first mode). This fixed level may be greater than the upper limit in some cases, but in this particular embodiment, this fixed level is less than the lower limit (and may be zero).

[0066] This primary drive signal P D causes resonance of the resonance structure 10 (i.e., the silicon ring) due to a step change in its level. The controller 44 is configured to measure the amplitude of the resulting resonance over time. In this particular embodiment, the controller 44 is connected to the output of the amplifier 32 and thus receives an amplified version of the primary pick-off signal P P from (i.e., from the sense or pick-off or "sense" electrode). At the end of a predetermined period, the vibration amplitude u(t) is measured from the primary pick-off signal P P .

[0067] Throughout a predetermined period during which the output of the AGC 34 is set to a predetermined level, the controller 44 counts the number of vibration cycles N that have occurred, i.e., counts how many "pulses" are present in the primary pick-off signal P P during that period.

[0068] As will be described in more detail below, the controller 44 determines Q from the measured vibration amplitude u(t) and the number of vibration cycles N, and supplies the determined Q to the compensator 36.

[0069] It will be understood that the amplitude u(t) of the vibration can be given by the formula of Equation 1 below.

[0070]

Equation

[0071] Equation 1: Vibration amplitude u(t) In the above formula, u(t) is the vibration amplitude at time t, U0 is the initial amplitude, ω is the angular frequency of the vibration, Q is the Q factor of the gyroscope 30, and φ is the phase offset.

[0072] The number of cycles N is given by Equation 2 below.

[0073]

Number

[0074] Equation 2: Vibration frequency N In the above equation, N is the vibration frequency, t is the time, and T is the vibration period as shown in Equation 3 below.

[0075]

Number

[0076] Equation 3: Vibration period T Then, the controller 44 can obtain the Q of the gyroscope 30 from the vibration amplitude u(t) and the number of vibration cycles N during a predetermined period by substituting Equation 2 and Equation 3 into Equation 1. By rearranging and simplifying the equation to solve for Q, it becomes Equation 4 below.

[0077]

Number

[0078] Equation 4: Q factor of the gyroscope 30 as a function of vibration amplitude and vibration frequency As outlined above, the obtained Q is supplied to the compensation device 36 by the controller 44. By using the correction mechanism 38, the compensation device 36 calculates the scale factor correction 37 from the obtained Q factor supplied by the controller 44. This scale factor correction 37 is supplied to the AGC 34, and the AGC 34 adjusts the level of the primary drive signal P D appropriately by modulating the gain of the primary drive amplifier 35.

[0079] Additionally, or alternatively, as indicated by the dashed line between 36 and 39 in FIG. 2, a scale factor correction 37’ may be applied to the velocity signal at 39 to provide a corrected velocity output (the “velocity” in FIG. 2) of the gyroscope 30. This is a more “direct” way of applying the scale factor and can be used instead of feeding the scale factor to the AGC 34. It is also possible to use both approaches in combination, although this can be more complex since the changes made at the AGC 34 affect the input at 39, and thus the compensation applied at 39 must take into account the compensation applied at the AGC 34, and vice versa.

[0080] The simulated performance of a gyroscope configured to determine its Q factor according to an embodiment of the present disclosure is outlined below with respect to FIGS. 3 - 6. Throughout FIGS. 3 - 6, various plots show the simulated operation of a gyroscope according to an embodiment of the present disclosure.

[0081] FIGS. 3 - 6 are graphs showing the simulated performance evaluation of the gyroscope 30 of FIG. 2. FIG. 3 shows an example of the modulation process, where the upper plot shows the primary drive (P D ) signal and the lower plot shows the primary pickoff (P P ) signal.

[0082] As seen in FIG. 3, the controller 44 first operates the gyroscope in a first normal mode, and the primary drive signal P D is applied with an amplitude controlled by the AGC 34, which is shown as pulses in the upper plot of FIG. 3. Intermittently, the controller 44 switches the gyroscope to a second mode to measure Q, and the AGC 34 sets the amplitude of the primary drive signal P D to zero.

[0083] When entering the second mode, as seen in the lower plot of FIG. 3, the primary pickoff signal P PIt begins to decay. As previously outlined, the controller 44 measures the vibration amplitude and the number of vibrations, and obtains an estimated value of unfiltered Q as shown in the graph of FIG. 4. These estimated values of Q tend to approach the actual value throughout each cycle, but are affected by noise.

[0084] By using a suitable filter to average the estimated values of Q over the cycles, the controller 44 obtains an estimated value of filtered Q as shown in FIG. 5 (the estimated value of Q is reset after each cycle). By continuously filtering over multiple cycles, the estimated value of Q tends to reach a specific value over time as seen in the graph of FIG. 6.

[0085] Thus, it will be understood that embodiments of the present disclosure provide an improved gyroscope and method of operating the same that can measure Q by overriding AGC during part of a cycle and observing the vibration amplitude and number of vibrations resulting as a consequence of the signal sensed from the pickoff electrode. Advantageously, this may enable Q to be measured during normal operation, while still being able to determine the angular velocity as before, and moreover, the contribution of changes in the primary drive due to variations in Q can be separated from variations due to magnet degradation, so that changes in the scale factor due to such magnet degradation can be compensated for appropriately. The present disclosure advantageously can also provide a mechanism for monitoring the overall health of the gyroscope so that maintenance or replacement of the gyroscope can be performed before device failure.

[0086] It should be understood that there are other sources of scale factor error that can be compensated for in a similar manner, either separately from or in addition to this process.

Claims

1. A vibrating structure gyroscope, comprising: a resonance structure configured to vibrate in response to a stimulus from a primary drive electrode; a drive system configured to vibrate the gyroscope at a resonance frequency, the drive system including the primary drive electrode configured to induce motion in the gyroscope and a primary sense electrode configured to sense the motion of the gyroscope; an automatic gain control device configured to change an amplitude of a drive signal applied to the primary drive electrode; a controller configured to operate the gyroscope, wherein, in a first operation mode, the automatic gain control device changes the amplitude of the drive signal between an operation range defined by a lower limit and an upper limit, and wherein, in a second operation mode, the automatic gain control device sets the amplitude of the drive signal to a predetermined level outside the operation range; the controller configured to operate the gyroscope to perform the above; and when the gyroscope is operating in the second operation mode, the controller measures an amplitude of a sense signal from the primary sense electrode after elapse of a predetermined period, determines a number of vibration cycles during the predetermined period, and determines a quality factor of the gyroscope from the measured amplitude and the number of vibration cycles. A vibrating structure gyroscope.

2. The vibrating structure gyroscope according to claim 1, wherein the predetermined level set for the amplitude in the second operation mode is smaller than the lower limit, and optionally, the predetermined level is zero.

3. The vibrating structure gyroscope according to claim 1 or 2, wherein the resonance structure includes a substantially planar ring structure.

4. The vibrating structure gyroscope according to any one of claims 1 to 3, wherein the resonance structure includes silicon.

5. The vibrating structure gyroscope according to any one of claims 1 to 4, further comprising an inductive gyroscope.

6. The vibrating structure gyroscope according to claim 5, further comprising a permanent magnet, wherein the resonance structure is disposed in a magnetic field of the permanent magnet.

7. The vibration structure gyroscope according to any one of claims 1 to 6, wherein the controller is configured to alternately perform the operation of the gyroscope between the first operation mode and the second operation mode.

8. The vibration structure gyroscope according to claim 7, wherein the controller is configured to obtain the quality factor over a plurality of operations of the automatic gain control device in the second operation mode.

9. The vibration structure gyroscope according to claim 8, wherein the controller is configured to apply a filter to continuously obtain a plurality of the quality factors to generate an estimated value of the filtered quality factor.

10. The vibration structure gyroscope according to any one of claims 1 to 9, comprising a drive control loop including the automatic gain control device and a phase-locked loop configured to maintain the phase and frequency of the drive signal provided to the primary drive electrode at the same phase and frequency as the resonance frequency of the resonance structure.

11. The vibration structure gyroscope according to any one of claims 1 to 10, comprising a compensation device configured to receive the obtained quality factor and output a scale factor correction based on the obtained quality factor.

12. Comprising a sensing system configured to sense the vibration of the gyroscope and output an angular velocity signal based on the sensed vibration, The vibration structure gyroscope according to claim 11, wherein the gyroscope is configured to apply the scale factor correction to the angular velocity signal to provide an output of the gyroscope.

13. A method of operating a vibration structure gyroscope, wherein the vibration structure gyroscope includes a resonance structure configured to vibrate in response to a stimulus from a primary drive electrode, a drive system configured to vibrate the gyroscope at a resonance frequency, the drive system including the primary drive electrode configured to induce motion in the gyroscope and a primary sense electrode configured to sense the motion of the gyroscope, an automatic gain control device configured to change an amplitude of a drive signal applied to the primary drive electrode, The method includes operating the gyroscope In the first operation mode, the automatic gain control device varies the amplitude of the drive signal between an operating range defined by a lower limit and an upper limit, and in the second operation mode, the automatic gain control device sets the amplitude of the drive signal to a predetermined level outside the operating range, and operates to perform the above, when operating the gyroscope in the second operation mode, the method includes measuring the amplitude of the sense signal from the primary sense electrode after a predetermined period has elapsed, determining the number of vibration cycles during the predetermined period, and determining the quality factor of the gyroscope from the measured amplitude and the number of vibration cycles, The method further includes. **Claim 14**: A calibration method for a vibrating structure gyroscope, comprising providing a vibrating structure gyroscope according to any one of Claims 1 to 12, determining the quality factor of the gyroscope during the startup process and / or normal operation of the gyroscope, storing information that enables quantification of scale factor correction from the quality factor based on the determined quality factor, The method includes.

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