Coriolis vibratory accelerometer system

A CVA system includes a sensor system including a pendulous element that rotates about a first axis via first flexures in response to an input acceleration provided along a second axis that is orthogonal with respect to the first axis. A torque-summing gimbal is coupled to the pendulous element via the first flexures and coupled to a housing via second flexures. The system further includes an accelerometer controller that monitors a pickoff signal of the rotation of the pendulous element from a first electrode coupled to the pendulous element and to provide a forcer signal to at least one second electrode coupled to the torque-summing gimbal to force the torque-summing gimbal to rotate about the second axis via the second flexures based on the pickoff signal to provide Coriolis force-rebalance of the pendulous element. The accelerometer controller can determine the input acceleration based on the rotation of the torque-summing gimbal.

TECHNICAL FIELD

This disclosure relates generally to sensor systems, and specifically to a Coriolis Vibratory Accelerometer (CVA) system.

BACKGROUND

In traditional electromagnetic and electrostatic force-rebalance instruments, such as an accelerometer, instability and non-repeatability of the characteristics of the control electronics are sources of error. For example, the voltages, currents, frequencies, or phases of the control electronics can be potential sources of error that can deleteriously affect the output of a respective electromagnetic and electrostatic force-rebalance instrument (e.g., rotation or acceleration). One example of an accelerometer currently deployed in inertial systems is the Pendulous Integrating Gyroscope Accelerometer (PIGA). The PIGA incorporates gyroscopic precession to force-rebalance to avoid the error sources associated with the characteristics of the control electronics. As a result, the PIGA is typically able to provide an accurate output (e.g., rotation or acceleration).

SUMMARY

A CVA system includes a sensor system including a pendulous element that rotates about a first axis via first flexures in response to an input acceleration provided along a second axis that is orthogonal with respect to the first axis. A torque-summing gimbal is coupled to the pendulous element via the first flexures and coupled to a housing via second flexures. The system further includes an accelerometer controller that monitors a pickoff signal of the rotation of the pendulous element from a first electrode coupled to the pendulous element and to provide a forcer signal to at least one second electrode coupled to the torque-summing gimbal to force the torque-summing gimbal to rotate about the second axis via the second flexures based on the pickoff signal to provide Coriolis force-rebalance of the pendulous element. The accelerometer controller can determine the input acceleration based on the rotation of the torque-summing gimbal.

Another example includes a method for measuring an input acceleration along a sensitive axis via a CVA system. The method includes providing an oscillating-mass forcer signal to at least one first electrode to drive an in-plane oscillatory motion of a plurality of oscillating-masses associated with a pendulous element of a sensor system. The method also includes monitoring a pickoff signal from at least one second electrode to determine a rotation of the pendulous element about a first axis via first flexures in response to an input acceleration provided along a second axis that is orthogonal with respect to the first axis. The method also includes generating a forcer signal based on the pickoff signal. The method also includes providing the forcer signal to at least one third electrode associated with a torque-summing gimbal of the sensor system to force the torque-summing gimbal to rotate in response to the pickoff signal to provide Coriolis force-rebalance of the pendulous element via the rotation of the torque-summing gimbal and the in-plane oscillatory motion of the oscillating-masses. The method further includes determining an input acceleration based on a velocity of the in-plane oscillatory motion of the oscillating-masses and an angular velocity of the rotation of the torque-summing gimbal.

Another example includes a CVA system. The system includes a sensor system. The sensor system includes a pendulous element configured to rotate about a first axis via first flexures in response to an input acceleration provided along a second axis that is orthogonal with respect to the first axis. The sensor system also includes a plurality of oscillating-masses coupled to the pendulous element via second flexures and being configured to oscillate in an in-plane oscillatory motion. The sensor system further includes a torque-summing gimbal coupled to the pendulous element via the first flexures and coupled to a housing via third flexures. The CVA system also includes an accelerometer controller. The accelerometer controller includes an oscillating-mass servo configured to provide an oscillating-mass forcer signal to at least one first electrode associated with the plurality of oscillating-masses to provide the in-plane oscillatory motion. The accelerometer controller also includes an angular rate servo configured to monitor a pickoff signal associated with the rotation of the pendulous element from at least one second electrode coupled to the pendulous element. The accelerometer controller also includes an acceleration rebalance servo configured to provide a forcer signal to at least one third electrode coupled to the torque-summing gimbal to force the torque-summing gimbal to rotate about the third flexures based on the pickoff signal to provide Coriolis force-rebalance of the pendulous element in response to the rotation of the torque-summing and the in-plane oscillatory motion of the oscillating masses. The accelerometer controller further includes an optical velocity detector configured to determine a velocity of the plurality of oscillating-masses and to determine an angular velocity of the torque-summing gimbal. The acceleration controller is configured to determine the input acceleration based on the velocity of the plurality of oscillating-masses and the angular velocity of the torque-summing gimbal.

DETAILED DESCRIPTION

This disclosure relates generally to sensor systems, and specifically to a Coriolis Vibratory Accelerometer (CVA) system. The CVA includes a sensor system and an accelerometer controller. The sensor system includes a pendulous element and a torque-summing gimbal. The pendulous element can have a set of flexures that are offset from a center of gravity of the sensor system to provide pendulosity of the pendulous element in response to an input acceleration along an input axis. As a result, the pendulous element can rotate about an axis orthogonal with the input acceleration via the flexures. The rotation of the pendulous element can be determined via a capacitive pickoff signal between a set of electrodes associated with the pendulous element and a corresponding set of electrodes coupled to a housing. The pickoff signal can thus correspond to the rotation of the pendulous element in response to the input acceleration. The pendulous element can also include a set of oscillating-masses that are provided a forcer signal to a corresponding set of electrodes to provide for an oscillatory motion of the oscillating-masses.

The torque-summing gimbal can be coupled to the pendulous element via a set of flexures, such as on-axis with respect to the input axis of the pendulous element to mitigate rotation of the torque-summing gimbal in response to input accelerations along an axis in the plane of the pendulous element and orthogonal to the input axis. The flexures supporting the torque summing gimbal can occupy the same plane as the combined center of mass of the pendulous element and torque summing gimbal. In this configuration, there may be no pendulosity and no rotation of the pendulous element and torque summing gimbal in response to acceleration along the orthogonal axis.

The torque-summing gimbal can be forced to oscillate about an axis (e.g., the axis associated with the input acceleration) orthogonal to the axis of rotation of the pendulous element. For example, in response to the pickoff signal associated with the pendulous element, the accelerometer controller can generate a forcer signal that is provided to a set of electrodes associated with the torque-summing gimbal to force the torque-summing gimbal to rotate about the axis. Therefore, in response to the in-plane oscillatory motion of the oscillating masses, and in response to the rotation of the torque-summing gimbal, such as in an oscillatory manner at a frequency that is the same as the in-plane oscillatory motion of the oscillating masses, the torque-summing gimbal can generate Coriolis accelerations on the respective oscillating masses that are configured to torque-rebalance the pendulous mass from the rotation caused by the input acceleration. In addition, the accelerometer controller can include a velocity detection component that is configured to determine a velocity of the oscillating-masses and an angular velocity of the torque-summing gimbal. As a result, the accelerometer controller can be configured to calculate an amplitude and polarity of the input acceleration in response to the determination of the velocity of the oscillating-masses and the angular velocity of the torque-summing gimbal.

FIG. 1illustrates an example of a Coriolis Vibratory Accelerometer (CVA) system100. The CVA system100can be implemented in any of a variety of applications with which accurate measurement of acceleration may be necessary, such as aviation, marine, or aerospace navigation. The CVA system100includes a sensor system120and an accelerometer controller140.

The sensor system120can be arranged in any of a variety of different physical configurations. In the example ofFIG. 1, the sensor system120includes a pendulous element160, a torque-summing gimbal170, a housing180, and velocity sensors190. The pendulous element160can include a set of flexures that occupy a plane that is offset from a center of gravity of the sensor system120, such that the pendulous element160can have pendulosity in response to an input acceleration along a first axis. As a result, the pendulous element160can be configured to rotate via the flexures in response to the input acceleration. As an example, the pendulous element160can include a set of electrodes that capacitively interact with a set of electrodes associated with the housing180, such that the rotation of the pendulous element160can be determined via a capacitive pickoff signal PO. In the example ofFIG. 1, the pickoff signals that are provided to the accelerometer controller140are demonstrated generally as a set of signals PO.

As an example, the pendulous element160can include a plurality of oscillating-masses that are driven via a first forcer signal (e.g., generated by the accelerometer controller140) applied to a set of electrodes to provide an in-plane oscillatory motion of the oscillating-masses. In the example ofFIG. 1, the forcer signals that are generated via the accelerometer controller140are demonstrated generally as a set of forcer signals FRC. For example, the oscillating-masses can include a pair or multiple pairs of oscillating-masses that oscillate concurrently in anti-parallel directions. For example, the in-plane oscillatory motion can be substantially in-plane with the pendulous element160. As another example, the pendulous element160can be coupled to the torque-summing gimbal180via a set of flexures, such that the torque-summing gimbal180can have an approximately concentric arrangement with respect to the pendulous element160. For example, the torque-summing gimbal180can be coupled to the housing200via another set of flexures, such as arranged in-plane with a center of mass of the sensor system120that can have an axis of rotation that is orthogonal with respect to the flexures associated with the pendulous element160. As an example, the accelerometer controller140can also be configured to generate a forcer signal FRC based on the pickoff signal PO provided from the pendulous element160. The forcer signal FRC can be provided to the torque-summing gimbal180via a set of electrodes coupled to the torque-summing gimbal180and to the housing200to force the rotation of the torque-summing gimbal180in response to the pickoff signal PO.

As described in greater detail herein, the accelerometer controller140can be configured to determine the input acceleration based on the angular velocity of the rotation of the torque-summing gimbal170and the velocity of the oscillatory motion of the oscillating-masses within the pendulous element160. As described herein, the term “rotate” and “rotation” with respect to the torque-summing gimbal170can refer to a forced oscillation of the torque-summing gimbal170about the first axis (e.g., corresponding to the input axis or sensitive axis). The rotation of the torque-summing gimbal170can therefore correspond to an angular rotation of the torque-summing gimbal170in one of two angular directions between which the torque-summing gimbal170is forced to oscillate. The angular velocity of the rotation in either of the two angular directions during the forced oscillation of the torque-summing gimbal170can be used along with the velocity of the oscillating masses to determine the input acceleration via the accelerometer controller140, as described in greater detail herein.

As an example, the accelerometer controller170can include a detection system (e.g., an optical detection system) that is configured to determine the velocity (e.g., angular velocity) of rotation of the torque-summing gimbal170and the linear velocity of the oscillating masses within the pendulous element. The detection is demonstrated in the example ofFIG. 1by a signal DET that can be associated with the determination of the velocity (e.g., angular velocity) of the torque-summing gimbal170and can also include an indication of the velocity of the oscillating-masses. For example, the sensor system120can include an optical detection system that can be configured to determine the velocity of the torque-summing gimbal170and the velocity of the oscillating-masses. As a result, the accelerometer controller140can calculate the input acceleration based on the velocity of the torque-summing gimbal170and the velocity of the oscillating-masses.

FIG. 2illustrates another example of a CVA system200,FIG. 3illustrates an example of a sensor system300,FIG. 4illustrates an example of a sensing element400,FIG. 5illustrates an example of an angular rate servo system500, andFIG. 6illustrates an example of an acceleration rebalance servo system600. The CVA system200can correspond to the CVA system100in the example ofFIG. 1. Therefore, reference is made to the example ofFIG. 1in the following description of the examples ofFIGS. 2-6. The CVA system200can be implemented in any of a variety of applications with which accurate measurement of acceleration may be necessary, such as aviation, marine, or aerospace navigation. The CVA system200includes a sensor system202and an accelerometer controller204.

The sensor system202can be arranged in any of a variety of different physical configurations. In the example ofFIG. 2, the sensor system202includes a sensing element201. The sensing element201includes a set of pendulous element pickoff/forcers electrodes208, a set of torque summing gimbal pickoff/forcer electrodes210, a set of oscillating-masses pickoff/forcer electrodes212, and a set of optical velocity sensors214. As an example, the set of electrodes212can correspond to the electrodes coupled to the housing464that interact with the electrodes472in the example ofFIG. 4. Similarly, the PM_PO electrodes206can correspond to electrodes coupled to the housing464that interact with the substantially planar electrodes460in the example ofFIG. 4, and the CF electrodes208can correspond to the electrodes coupled to the housing464that interact with the electrodes478(e.g., the second set of electrodes658in the example ofFIG. 6).

The accelerometer controller204includes an angular rate servo216that is configured to provide one or more force-rebalance signals AR_FRB to the PO/F electrodes208and receives one or more pickoff signals PM_PO from the PO/F electrodes206. For example, the force-rebalance signal(s) AR_FRB and the pickoff signal(s) PM_PO can correspond to a portion of the forcer signals FRC and the pickoff signals PO in the example ofFIG. 1, respectively. Therefore, the pickoff signal(s) PM_PO can correspond to rotation of the pendulous element160in the example ofFIG. 1. In response to the pickoff signal(s) PM_PO, the angular rate servo216is configured to generate the force-rebalance signal(s) AR_FRB to substantially null the position of the pendulous element160in response to the oscillation of the pendulous element160(e.g., in response to the angular rate input as described herein). Additionally, the amplitude of the force-rebalance signal(s) AR_FRB can be implemented by the accelerometer controller204to determine an angular rate of rotation of the sensor system202, such as about the input axis. (e.g., the X-axis in the example ofFIG. 4). For example, the angular rate servo216can be configured to demodulate an oscillation frequency corresponding to the oscillation of the pendulous element160resulting from angular rate to generate the force-rebalance signal(s) AR_FRB.

The accelerometer controller204also includes an oscillating-mass servo220that is configured to provide one or more forcer signals OM_F to the electrodes212associated with the oscillating-masses212and receives one or more pickoff signals OM_PO from the electrodes212. For example, the forcer signal(s) OM_F and the pickoff signal(s) OM_PO can correspond to a portion of the forcer signals FRC and the pickoff signals PO in the example ofFIG. 1, respectively. As an example, the forcer signal(s) OM_F can be provided to the electrodes212to provide for the in-plane oscillatory motion of the oscillating-masses212, and the pickoff signal(s) OM_V can be indicative of the oscillatory motion of the oscillating-masses212. In the example ofFIG. 2, the accelerometer controller204also includes a frequency generator222that is configured to provide a control frequency signal F_CF to the oscillating-masses212such as in a kilohertz range. A +Vdc bias voltage and a Vac carrier signal is applied to the sensing element by the bias voltage and carrier signal generator228. The bias voltage and the carrier signal are used by all capacitive pickoff and electrostatic forcers.

Referring to the example ofFIG. 3, the sensor system300can correspond to the sensor system120in the example ofFIG. 1. Therefore, reference is made to the example ofFIG. 1in the description of the following description of the example ofFIG. 3. The sensor system300is demonstrated in the example ofFIG. 3by example, and is not intended to be limited with respect to physical arrangement. Thus, the sensor system300can be physically arranged and fabricated in a variety of different ways. For example, the sensor system can be fabricated and assembled using MEMS technology. As an example, the sensor system300may be comprised of an integrated optic chip306and MEMS sensor308. The individual layers of the MEMS sensor are illustrated inFIG. 3. The top and bottom SOI wafers (e.g., only the top wafer is illustrated in the example ofFIG. 3) are comprised of a handle layer310, a buried oxide layer320, and a device layer340. The device layer340contains the pickoff and forcer electrodes illustrated in the sensing element201in the example ofFIG. 2. The center layer is fabricated from a prime silicon wafer350and a deposited oxide layer360that determines the capacitive gap for the pickoffs and forcers.

Referring to the example ofFIG. 4, the sensing element400can correspond to the sensing element206in the example ofFIG. 2. The sensor system400is demonstrated in the example ofFIG. 4by example and is not intended to be limited with respect to the physical arrangement. Thus, the sensor system400can be physically arranged and fabricated in a variety of different ways, such as illustrated inFIG. 3.

The sensor system400includes three separate views, demonstrated in the example ofFIG. 4as a first view452, a second view454, and a third view456with respect to a three-dimensional Cartesian coordinate system482. Therefore, the first view452corresponds to a “front” or “top” view, while the second view454and third view456each correspond to “side” views. The sensor system400includes a pair of oscillating-masses458, a pendulous element460, and a torque-summing gimbal462that are coupled to a housing frame464and which are arranged in a substantially concentric arrangement with respect to each other. The housing frame464is demonstrated as substantially surrounding the oscillating-masses458and the pendulous element460. A separate portion of the housing464covers the torque-summing gimbal462and the frame464. However, the housing464can also include planar portions that are “above” and “below” the oscillating-masses458, the pendulous element460, and the torque-summing gimbal462in XY-planes that are offset from the oscillating-masses458, the pendulous element460, and the torque-summing gimbal462along the Z-axis. For example, the housing464can include electrodes to interact with the oscillating-masses458, the pendulous element460, and the torque-summing gimbal462, as described in greater detail herein.

In the example ofFIG. 4, the oscillating-masses458are coupled to the pendulous element460via a set of flexures466, the pendulous element460is coupled to the torque-summing gimbal462via a set of flexures468, and the torque-summing gimbal462is coupled to the housing464via a set of flexures470. The flexures466are arranged to provide for an anti-parallel oscillatory motion of the oscillating-masses458that is in-plane with respect to the opposing surfaces of the pendulous element460(e.g., in the XY-plane in a neutral position of the pendulous element460). In the example ofFIG. 4, the oscillating-masses458include electrodes472extending from at least one of the planar surfaces (e.g., the XY-plane), such that the electrodes472are arranged in a “tooth” drive arrangement, as described in greater detail herein.

An example of the anti-parallel oscillatory motion of the oscillating-masses458is demonstrated in the example ofFIG. 4. As demonstrated in the example ofFIG. 4, the oscillating-masses458are driven with substantially equal velocity and are driven oppositely with respect to the in-plane oscillatory motion. The example ofFIG. 4demonstrates one phase, such that an opposite phase occurs in which the oscillating-masses458switch directions and are moved to opposite extreme locations via the electrodes472. Thus, the oscillating-masses458are driven with controlled velocity by the accelerometer controller204between opposite respective extreme locations in-plane with the pendulous element460.

In the example ofFIG. 4, the flexures468are arranged along the Y-axis to provide for rotation of the pendulous element460about the Y-axis. As demonstrated in the third view456, the flexures468are arranged in a plane that is offset from a center of gravity474of the sensing element400. As a result, in response to an input acceleration provided along the X-axis corresponding to a sensitive axis of the sensor system202, the pendulous element460can exhibit pendulosity to provide for a rotation of the pendulous element460about the flexures468. The pendulous element460includes electrodes476, demonstrated as “PO/F ELECTRODES”, that are arranged on the surface of the pendulous element460in the XY-plane on opposite extreme portions of the pendulous element460with respect to the rotation about the flexures468. As an example, the pendulous element460can include the electrodes476on each of the opposite XY-planar surfaces. In response to the rotation of the pendulous element460, the electrodes476can capacitively react with electrodes coupled to opposing surfaces of the housing (not shown in the example ofFIG. 4) to provide a capacitive pickoff signal (e.g., corresponding to the pickoff signal PO in the example ofFIG. 1). Therefore, the accelerometer controller140can be provided an indication of the rotation of the pendulous element460about the flexures468via the pickoff signal PO.

The flexures470are arranged along the X-axis to provide for rotation of the torque-summing gimbal462about the X-axis. As demonstrated in the second view454, the flexures470are arranged in-plane with the center of gravity474of the sensing element400to minimize pendulosity of the torque-summing gimbal462and minimize rotation of the torque summing gimbal in response to acceleration along the Y-axis. The torque-summing gimbal462includes electrodes478, demonstrated as “CF ELECTRODES”, arranged as “fingers” integral with the torque-summing gimbal462in the XY-plane on opposite portions of an approximate XY-vector (e.g., +X, +Y and −X, −Y) of the torque-summing gimbal462. In response to forcer signals FRC provided to the electrodes658inFIG. 6, the torque-summing gimbal462can rotate (e.g., oscillate) about the X-axis. For example, the forcer signals FRC can be generated by the accelerometer controller140based on the pickoff signal PO provided in response to the rotation of the pendulous element460. The forcer signals FRC can thus force the torque-summing gimbal462to oscillate, thus generating Coriolis accelerations on the oscillating masses resulting in a torque to rebalance the pendulous element460and thereby null the pendulous element pickoff.

The example ofFIG. 4demonstrates an example of the electrodes478. The example ofFIG. 5demonstrates a window502corresponding to the example ofFIG. 4.FIG. 6illustrates an example diagram650of torque-summing gimbal electrodes. The diagram650includes a view652of the torque-summing gimbal electrodes (e.g., demonstrated as a cross-sectional view of the sensing element400in the example ofFIG. 4).

In the example ofFIG. 6, the torque-summing gimbal electrodes include a first set of electrodes656and corresponding second sets of electrodes658. The first set of electrodes656can correspond to the electrodes478inFIG. 4that are integral to the torque-summing gimbal462, and the second sets of electrodes490can correspond to sets of electrodes that are coupled to the housing464. As demonstrated in the example ofFIG. 6, the sets of electrodes656and658are demonstrated as being interdigitated with each other in an out-of-plane “comb” drive configuration. As a result, the force-rebalance signal FRC that is provided to the second set of electrodes658can electrostatically force the first set of electrodes656of the torque-summing gimbal462to rotate (e.g. oscillate).

Referring to the example ofFIG. 5, the angular rate servo system500includes a sensing element502and an angular rate servo504. The sensing element502includes a pendulous element that can correspond to the pendulous element460inFIG. 4. The angular rate servo system also includes an angular rate servo504that can correspond to the angular rate servo216inFIG. 2. The angular rate servo504includes a pickoff amplifier512, a carrier demodulator514, a narrow bandpass filter516and an integral gain amplifier518. The angular rate servo nulls the angular oscillation of the pendulous element at the oscillating masses frequency due to angular rate about the input axis of the sensor system200inFIG. 1. The cancelation of the oscillation of the pendulous element by the angular rate servo eliminates this error source in the measurement of the velocity of the oscillating masses, The force-rebalance signal of the angular rate servo may be used as an estimate of the angular rate about the sensing element's input axis510

Referring to the example ofFIG. 6, the acceleration rebalance servo system includes a sensing element602and an acceleration rebalance servo604. The sensing element602includes pendulous element612that can correspond to pendulous element460inFIG. 4and a torque summing gimbal610that can correspond to the torque summing gimbal462inFIG. 4. The acceleration rebalance servo system also includes an acceleration rebalance servo604that can correspond to the acceleration rebalance servo218inFIG. 2. The acceleration rebalance servo604includes a torque summing gimbal servo606and an acceleration sensing servo608. The torque summing gimbal servo606includes a pickoff amplifier616, a carrier demodulator618, a low pass filter620, a summing point622, and an integral gain amplifier624. The elements616,618,620,622and624of the torque summing gimbal servo, restricts the torque summing gimbal's rotation (e.g. oscillating) to respond only to an offset (e.g., slew) signal applied to the summing point622by the acceleration sensing servo608, and a digital-to-analog converter (DAC)634. The acceleration rebalance servo604also includes an acceleration sensing servo608. The acceleration sensing servo includes a pickoff amplifier626, a carrier demodulator628, a high pass filter630, an integral gain amplifier632and a DAC634. The elements626,628,630,632and634of the acceleration rebalance servo force the torque summing gimbal610to rotate (e.g. oscillate) in response to rotation of the pendulous element612in response to acceleration along the input axis of the sensing system200inFIG. 1.

As an example, the acceleration controller204can be configured to determine the input acceleration a based on a CVA torque rebalance equation, described as follows:
α=(m2*L2)+(m3*L3)*(2*V1*V2)/(m1*L1)  Equation 1

Where: α is the input acceleration;

m1is the mass of the pendulous element;

L1is the pendulous arm of the pendulous element;

m2and m3correspond to masses of the oscillating masses;

L2and L3correspond to the lever arms of the oscillating masses, respectively;

Φ is the angular displacement of the torque-summing gimbal;

x is the linear displacement of the oscillating masses;

V1=dΦ/dt is the angular velocity of the torque-summing gimbal;

V2=dx/dt is the linear velocity of the oscillating masses, such that (2*V1*V2) corresponds to the Coriolis acceleration on the oscillating masses.

Therefore, Equation 1 demonstrates that the input acceleration can be calculated by the acceleration controller204. Referring to the example ofFIG. 2, the accelerometer controller204further includes optical velocity detector electronics224configured to determine the input acceleration based on the angular velocity of the torque-summing gimbal210and the linear velocity of the oscillating masses212. For example, the optical velocity sensors214can be arranged as any of a variety of integrated optical system306as illustrated inFIG. 3(e.g., a laser Doppler vibrometer (LDV), a self-mixing laser diode vibrometer, or a fiber-optic Sagnac vibrometer) to determine the velocity (e.g., angular velocity) of the torque-summing gimbal210and linear velocity of the oscillating masses212. The detection is demonstrated in the example ofFIG. 2by optical signals OPTDETIONthat can be associated with the determination of the velocity (e.g., angular velocity) of the torque-summing gimbal210and include the velocity of the oscillating-masses212. For example, the optical signals OPTDETIONcan be provided incident on the torque-summing gimbal210and/or the oscillating-masses212to provide an indication of velocity based on reflection of the optical signals OPTDETIONwith respect to the optical velocity sensors214. As a result, the accelerometer controller204can calculate the input acceleration based on the velocity of the torque-summing gimbal210and the velocity of the oscillating-masses212.

In addition, the optical velocity sensor214can be implemented to provide for self-integration of the determination of the input acceleration. For example, based on the predetermined physical characteristics of the torque-summing gimbal210, the measured rotation of the torque-summing gimbal212can be implemented by the accelerometer controller204to calculate the total angular displacement (sum of plus and minus angles for the same polarity of input acceleration) of the torque-summing gimbal210about the respective flexures360. Based on the known changes to the angular displacement of the torque-summing gimbal210, as determined by the optical velocity sensor214in concert with the processing of the accelerometer controller204, the accelerometer controller204can provide for self-integration of the input acceleration acting upon the sensor system202(e.g., via the feedback of the oscillating-mass servo220) based on measuring the total angular displacement of the torque-summing gimbal210while compensating for any change in the velocity of the oscillating-masses212, such as based on the predetermined physical characteristics of the sensor system202, as well as the linear velocity of the oscillating masses212and the angular velocity of the torque-summing gimbal210. As a result, the CVA system100, as described herein, can exhibit improved reliability and reduced cost relative to other types of accelerometers (e.g., Pendulous Integrating Gyroscope Accelerometer (PIGA) or Specific Integrating Force Receiver (SIFR). The CVA system100can also provide for a greater accuracy based on calculating the input acceleration via determined (e.g., optically determined) velocity characteristics, as opposed to other accelerometers that rely on electrostatic or electromagnetic force-rebalance of the input acceleration. Furthermore, as described herein, the CVA system100can also perform angular rate detection and self-integration with little additional firmware manipulation of the accelerometer controller.

FIG. 7illustrates an example of an oscillating-mass servo system700. The oscillating-mass servo system700includes a sensing element702and an oscillating mass servo704that can correspond to the oscillating-mass servo220in the example ofFIG. 2.

The oscillating-mass servo704includes a pickoff amplifier712, carrier demodulator714, summing point716, integral gain718, triangle wave generator720, and DAC722. The pickoff amplifier712is coupled to sets of electrodes708that interact with the oscillating-masses706. The oscillating-masses706and the sets of electrodes708are demonstrated as a “tooth” drive oriented based on a Cartesian coordinate system730relative to the Cartesian coordinate system482in the example ofFIG. 4. The sets of electrodes706can correspond to the electrodes212in the example ofFIG. 2. The integral gain component718is configured to provide the forcer signals OM_F to null the pickoff output of the pickoff amplifier712having received the pickoff signals OM_PO, demonstrated collectively in the example ofFIG. 2as signals “OM_PO”. As an example, the electrodes708can correspond to a common set of electrodes for the forcer and pickoff signals OM_F and OM_PO, respectively, or can correspond to dedicated respective sets of electrodes for the forcer and pickoff signals OM_F and OM_PO, respectively. In addition, the oscillating-masses706are provided the carrier frequency signal F_CF and +Vdc bias voltage, as described previously in the example ofFIG. 2.

The pickoff amplifier712can provide the received pickoff signal OM_PO to a carrier demodulator714that is configured to demodulate the carrier frequency signal F_CF from the pickoff signal(s) OM_PO. The demodulated pickoff signal OM_PO is provided to a summing component716. The summing component716is configured to add a triangular wave signal, demonstrated at720, to the demodulated pickoff signal OM_PO. In the example ofFIG. 7, the triangular wave signal724has an amplitude that is centered on approximately zero. The summing component716therefore provides the summed signal to an integral gain component718that is configured to provide the integrated forcer signal OM_F signal to the to the electrodes708to provide the oscillatory motion of the oscillating-masses706. In the example ofFIG. 7, the triangular wave signal724is generated by firmware applied to the DAC722that generates the triangular wave signal724as having a substantially linear positive and negative slew rate (e.g., equal and opposite) to provide for a substantially constant velocity of the oscillating-masses706in the +Y and −Y directions. Therefore, the oscillating-mass servo704can provide for feedback control of the oscillatory motion of the oscillating-masses706to maintain the substantially constant velocity. Accordingly, because the oscillatory motion of the oscillating-masses706is based on a substantially constant slew rate triangular wave signal724, the oscillating-mass servo704can be subjected to substantially less velocity noise due for example to external vibration in operating the associated control loop, and the velocity of the oscillating-mass252can be more easily determined for calculation of the input acceleration, as described herein.

FIGS. 8A and 8Billustrate an example diagram800of Coriolis force-rebalance of a sensor system. The diagram800includes a first phase802, illustrated inFIG. 8A, and a second phase804, illustrated inFIG. 8B, corresponding to respective alternating phases of the in-plane oscillatory motion of the oscillating masses, demonstrated in the example ofFIGS. 8A and 8Bas oscillating masses806and808. The diagram800demonstrates a simplified plan view of the sensor system202in each of the phases802and804.

The pendulum is shown to be below the plane of the sensing element inFIGS. 8A and 8Billustrated in diagram800. The diagram800demonstrates an input acceleration810in the +X direction, which will result in rotation of the pendulous element, demonstrated at812, about the +Y-axis via flexures814. In the first phase802, the first oscillating mass806is moving in the −Y direction at a velocity V1and the oscillating mass808is moving in the +Y direction at a velocity −V2. In response to the pickoff signal PO resulting from the rotation of the pendulous element812, the acceleration controller204can generate a forcer signal FRC that is provided to the electrodes (e.g. associated with the housing), to force the torque-summing gimbal, demonstrated at816, to rotate about flexures818.

The rotation of the torque-summing gimbal816can be such to provide an angular velocity of the torque-summing gimbal816about the −X-axis in a manner that is at the same frequency and in a 180° phase relationship with the in-plane oscillatory motion of the oscillating masses806and808. The phase relationship is determined by the polarity of the pendulous element pickoff. The rotation of the torque-summing gimbal816is demonstrated in the first phase802at820about the flexures818and is thus counter-clockwise looking along the +X-axis. As a result of the combination of the in-plane oscillatory motion of the oscillating masses806and808and the counter-clockwise rotation of the torque-summing gimbal816in the first phase802, a Coriolis acceleration is generated at each of the oscillating masses806and808. The Coriolis acceleration of the oscillating masses generate forces demonstrated in the example ofFIG. 8Aas F1in the +Z direction and as −F2in the −Z direction. The Coriolis forces F1and −F2therefore provide a torque-rebalance of the pendulous element812to counteract the torque on the pendulous element812resulting from the input acceleration810. The rotation of the pendulous element812resulting from the Coriolis torque-rebalance based on the Coriolis forces F1and −F2is demonstrated at828.

In the second phase804, the first oscillating mass806is moving in the +Y direction at a velocity +V1and the oscillating mass808is moving in the −Y direction at a velocity −V2. In response to the pickoff signal PO resulting from the rotation of the pendulous element812, the acceleration controller204can continue to provide the forcer signal FRC that is provided to the electrodes (e.g., associated with the housing), to force the torque-summing gimbal816to rotate about flexures818. In the second phase804, the rotation of the torque-summing gimbal816is reversed like the alternate phase of the in-plane oscillatory motion of the oscillating masses806and808. The rotation of the torque-summing gimbal816is demonstrated in the second phase804at830about the flexures818and is thus clockwise looking along the +X-axis. As a result of the combination of the in-plane oscillatory motion of the oscillating masses806and808and the clockwise rotation of the torque-summing gimbal816in the second phase804, a Coriolis acceleration is generated at each of the oscillating masses806and808, with the resultant forces demonstrated in the example ofFIG. 8Bas +F1in the +Z direction and as −F2in the −Z direction. The Coriolis forces +F1and −F2therefore continue to provide the torque-rebalance of the pendulous element812to counteract the torque on the pendulous element812resulting from the input acceleration810. The rotation of the pendulous element812resulting from the Coriolis torque-rebalance based on the Coriolis forces +F1and −F2is demonstrated at828in the second phase804, which is in the same rotational direction as the Coriolis torque-rebalance in the first phase802.

FIG. 9illustrates an example of a method900for measuring an input acceleration along a sensitive axis (e.g., the X-axis) via a CVA system. At902, an oscillating-mass forcer signal (e.g., the forcer signal OM_F inFIG. 2) is provided to at least one first electrode (e.g., the electrodes472inFIG. 4) to drive an in-plane oscillatory motion of a plurality of oscillating-masses (e.g., the oscillating-masses458). At904, a pickoff signal (e.g., the pickoff signal PM_PO inFIG. 2) is monitored from at least one second electrode (e.g., the PO/F electrodes208) to determine a rotation of a pendulous element (e.g., the pendulous element460about a first axis (e.g., the Y-axis) via first flexures (e.g., the flexures468) in response to the input acceleration provided along a second axis (e.g., the X-axis) that is orthogonal with respect to the first axis. At906, a forcer signal (e.g., the torque-rebalance signal TSG_T) is generated based on the pendulous element pickoff signal. At908, the forcer signal is provided to at least one third electrode (e.g., the TSG electrodes210) associated with a torque-summing gimbal (e.g., the torque-summing gimbal462) to force the torque-summing gimbal to rotate (e.g. oscillate) in response to the pickoff signal to provide Coriolis torque-rebalance of the pendulous element via the oscillatory angular velocity of the torque-summing gimbal and the in-plane oscillatory velocity of the oscillating masses. At910, an input acceleration is determined based on a velocity of the in-plane oscillatory motion of the oscillating-masses and the oscillatory angular velocity of the rotation of the torque-summing gimbal.