MEMS sensor with decoupled drive system

In a first aspect, the angular rate sensor comprises a substrate and a rotating structure anchored to the substrate. The angular rate sensor also includes a drive mass anchored to the substrate and an element coupling the drive mass and the rotating structure. The angular rate sensor further includes an actuator for driving the drive mass into oscillation along a first axis in plane to the substrate and for driving the rotating structure into rotational oscillation around a second axis normal to the substrate; a first transducer to sense the motion of the rotating structure in response to a Coriolis force in a sense mode; and a second transducer to sense the motion of the sensor during a drive mode. In a second aspect the angular rate sensor comprises a substrate and two shear masses which are parallel to the substrate and anchored to the substrate via flexible elements.

FIELD OF THE INVENTION

The present invention relates generally to angular velocity sensors and more particularly relates to angular velocity sensors that include guided mass systems.

BACKGROUND

Sensing of angular velocity is frequently performed using vibratory rate gyroscopes. Vibratory rate gyroscopes broadly function by driving the sensor into a first motion and measuring a second motion of the sensor that is responsive to both the first motion and the angular velocity to be sensed.

Accordingly, what is desired is to provide a system and method that overcomes the above issues. The present invention addresses such a need.

SUMMARY

An angular rate sensor is disclosed. In a first aspect, the angular rate sensor comprises a substrate and a rotating structure anchored to the substrate. The angular rate sensor also includes a drive mass anchored to the substrate and an element coupling the drive mass and the rotating structure. The angular rate sensor further includes an actuator for driving the drive mass into oscillation along a first axis in plane to the substrate and for driving the rotating structure into rotational oscillation around a second axis normal to the substrate; a first transducer to sense the motion of the rotating structure in response to a Coriolis force in a sense mode; and a second transducer to sense the motion of the sensor during a drive mode.

In a second aspect, the angular rate sensor comprises a substrate and a first shear mass and a second shear mass which are parallel to the substrate and anchored to the substrate via at least a first plurality of flexible elements. The angular rate sensor further includes a drive mass which is parallel to the substrate and anchored to the substrate via at least a second plurality of flexible elements.

DETAILED DESCRIPTION

FIG. 1Aillustrates a first embodiment of a single axis gyroscope100ain accordance with the present invention. The single axis gyroscope is disposed in an X-Y plane parallel to a substrate101and comprises a drive system110, a sense system159aand a coupling element131. The drive system110includes a drive mass130, an electrostatic actuator109, two drive springs105a-b, an anchor120and two drive-sense electrodes106a-b. The drive springs105a-band the anchor120act as a suspension system for the drive mass. The sense system159acomprises a rotating proof mass150a, a pivot spring115, an anchor140and two capacitive sense electrodes151aand151b. Finally, the drive system110and the sense system159aare coupled by a coupling spring131. In an embodiment, the suspension system is stiffer than the coupling spring131while the drive mass130is rotating out of plane.

The drive mass130is coupled to the substrate through spring elements105a-band the anchor120. In the drive operation of the single axis gyroscope100a, electrostatic forces are applied to the drive mass130via the electrostatic actuator109, and the motion of drive mass130in Y direction is detected by electrostatic transducers106aand106bthat are called drive-sense electrodes. The detected drive motion can be transferred to circuitry to be used to control the mechanical amplitude of drive mass130in a closed loop operation.

Although electrostatic actuators and transducers will be described throughout this specification, one of ordinary skill in the art recognizes that a variety of actuators could be utilized for this function and that use would be within the spirit and scope of the present invention. For example, the actuators or transducers could be piezoelectric, thermal or electromagnetic or the like.

The drive mass130is driven in the Y direction by the electrostatic actuator109at a certain frequency, which is referred to as a drive frequency. While drive mass130is driven in the Y direction, a moment around the Z-axis and a Y-direction force are applied to the rotating proof mass150athrough the coupling spring131. If the pivot spring115is very stiff in the Y direction, the rotating proof mass150arotates around an axis that is parallel to the Z-axis due to the applied moment. The described motion of the drive mass130and rotating proof mass150ais referred to as a drive motion.

When the gyroscope100ais subject to an angular velocity about a roll-input axis in the Y-direction that is in the plane of the substrate101and orthogonal to the X-direction will cause Coriolis forces to act on the rotating proof mass150ain the Z-direction. The Coriolis forces cause the rotating proof mass150ato rotate out-of-plane about the roll-sense axis which is parallel to the X-direction. The amplitude of the rotation of the rotating proof mass150ais proportional to the angular velocity about the roll-input axis and also mechanical drive amplitude of the rotating proof mass150a. The capacitive sense electrodes151aand151b, which are placed on the substrate101under the rotating proof mass150a, are used to detect the rotation of the rotating proof mass150aabout the roll-sense axis. This rotation provides a measure of the angular velocity about the roll-input axis. Although the capacitive electrodes151aand151bare given as transducers to detect the rotation of the rotating proof mass150aaround the roll-sense axis, various types of transducers could be utilized in the present invention. For example, the capacitive electrodes151a-bcould be also piezoelectric or optical or the like and its use would be within the spirit and scope of the present invention.

As it is given inFIGS. 1A and 1B, the drive mass130is separated from the rotating proof mass150aand the electrostatic actuators109are attached to the drive mass130. A benefit of this approach is to eliminate the effect of the non-idealities of the electrostatic actuator109on the rotating proof mass150a. The non-idealities of the electrostatic actuator may be due to the fabrication imperfections, like sidewall angle during deep reactive ion etching, or built-in stresses due to the environmental effects.

As an example, the electrostatic forces generated by a non-ideal electrostatic actuator may not be only in-plane but also out-of plane, the out-of plane non-ideal forces could result in unwanted out-of plane motion and rotation of the rotating proof mass150aaround its sensitive axis. The unwanted rotation of the rotating proof mass150aaround its sensitive axis would lead to erroneous motion which can be detected by the capacitive sense electrodes151a-bresulting in an error in the measurement of angular velocity.

On the other hand, inFIGS. 1A and 1B, drive mass130is coupled to the anchor120via springs105a-bwhich are very stiff in Z direction. As a result, the motion of drive mass130due to the non-ideal out-of plane electrostatic forces by actuator109is minimized. Consequently, the non-ideal forces are not transferred to the proof mass150a, and measurement errors are reduced.

InFIG. 1A, the coupling spring131, which is used to transfer the linear Y direction motion of the drive mass130to the rotation of the proof mass150a, can be made very stiff in Y-direction, but act as a pivot for rotation about z-axis or a torsion spring. Using a flexure as a coupling spring131in embodiment100acan be an option to satisfy those compliance conditions.

If the coupling spring131is made very stiff in Y-direction, but act as a pivot for rotation about z-axis, the whole single axis gyroscope100awould act as a single Degree of Freedom (DOF) mechanical system in the drive motion. The Y-direction motion of drive mass130is converted to in-plane rotation of the proof mass150aaround an axis parallel to the Z direction. The amount of rotation of proof mass150depends on the ratio of the length of the coupling spring to the radius of rotation of the proof mass150awith respect to the center of its rotation. The Y-direction motion is either amplified or attenuated depending on the ratio. Moreover, the drive-sense electrodes106a-bcan be placed on the drive mass130without effecting the closed loop drive operation.

FIG. 1Billustrates a second embodiment of a single axis gyroscope in accordance with the present invention. In the embodiment shown inFIG. 1B, the coupling spring131is compliant in the Y-direction and can be designed so that single axis gyroscope100bacts as a two DOF system in the drive motion. In that configuration, the sense system159bcan be designed as a vibration absorber of the drive mass130. As a result, small motion on drive mass130can be amplified to get bigger motion on the sense mass150a. For a vibration absorber configuration, it is necessary that drive-sense electrodes106a-bto be connected to the rotating proof-mass150aas it is shown inFIG. 1B. The connection is necessary to allow the rotational motion of rotating proof mass150aat a certain mechanical amplitude around the Z axis (the main component of the drive motion) to maximize the sensitivity of the gyroscope100b.

The small motion on the drive mass130is beneficial for area optimization. If the drive mass130has small drive motion, the electrostatic actuator gaps could be kept small, which will result in area savings. Moreover, the small drive motion is beneficial to minimize the spring softening, squeeze film damping and the non-linearity effects.

To explain the operation of the gyroscope100bin more detail refer now toFIGS. 1C and 1D.FIG. 1Cis a simple block diagram of the gyroscope100b, the reference numerals which conform to those ofFIG. 1B. It is desirable in the gyroscope100bthat the drive mass130moves less than the sense mass150a. The minimization of motion of130is accomplished by tuning the coupling spring kc (131) such that it is at least an order of magnitude more flexible than the springs kd (105a/105b) and ks (115).

To explain the tuning of kc spring in more detail, bode plots of the transfer functions Xd/Fd and Xs/Fd are shown inFIG. 1Dwhere Xd is the movement of the drive mass130in a first direction, Xs is the movement the sense mass150ain a second direction and Fd is the force caused by the actuator109on the drive mass130. InFIG. 1D, the top plot shows the amplitude vs. frequency information and the bottom plot shows phase vs. frequency.

Xd/Fd transfer function has two peaks, and one zero. A first peak represents a motion of the drive mass (md) in the common mode shape, and the second peak represents a motion of the drive mass (md) in differential mode shape. In an embodiment, the flexibility of the coupling spring kc is such that the transfer function Xs/Fd is greater than Xd/Fd at a specific frequency range of interest. As an example inFIG. 1D, an expansion of a specific region has been shown. Based on the 2-DOF mechanical system dynamics, if the kc spring is sufficiently compliant compared to the ks and kd, the separation between first peak and zero is minimized in Xd/Fd transfer function. So, the amplitude of the first peak is attenuated. On the other hand Xs/Fd transfer function is not affected by the zero due to the 2-DOF system characteristics and its amplitude remains constant in the frequency range of interest. As a result, by placing the zero close to the first peak in Xd/Fd, the amplitude difference between drive mass and sense mass is obtained.

FIG. 2illustrates a third embodiment of a single axis gyroscope200in accordance with the present invention. In this embodiment, the sense system160has some differences compared to the sense system159awhich is shown inFIG. 1A. The sense system160comprises a circular proof mass150b, instead of a rectangular proof mass150agiven inFIG. 1A. Moreover, the proof mass150bis coupled to the substrate via two pivot springs115aand115band the anchor141. The drive system110is similar to the embodiment given inFIG. 1A. Similar to the single axis gyroscopes shown inFIGS. 1A and 1B, the single axis gyroscope200is driven via electrostatic actuator109attached to the drive mass130.

When the drive mass130is driven in Y direction, the proof mass150brotates around Z axis. The amplitude of the drive motion of the proof mass150bdepends on the drive mass130motion and the coupling spring131stiffness as it was explained previously. The amplitude of drive motion of the proof mass150bis detected by the drive sense electrodes106aand106b

An angular velocity about a roll-input axis in the Y-direction that is in the plane of the substrate101and orthogonal to the X-direction will cause Coriolis forces to act on the proof mass150bin the Z-direction. The Coriolis forces cause the proof mass150bto rotate out-of-plane about the roll-sense axis which is parallel to the X-direction. The amplitude of the rotation of the proof mass150bis proportional to the angular velocity about the roll-input axis. The capacitive sense electrodes151aand151b, which are placed on the substrate101under the proof mass150b, are used to detect the rotation of the proof mass150babout the roll-sense axis. This rotation provides a measure of the angular velocity about the roll-input axis.

FIG. 3illustrates a fourth embodiment of a single-axis gyroscope300configuration in accordance with the present invention. The gyroscope configuration300includes two drive systems110aand110b, two coupling springs131aand131b, a rotating structure161and two yaw proof mass systems180aand180b. Drive systems110aand110bare similar to the drive system110given inFIG. 1A,FIG. 1BandFIG. 2. Drive systems110a-bboth include anchors120a-b, drive springs105a-d, drive masses130a-b, drive-sense combs106aand106band electrostatic actuators109a-b. Yaw proof mass systems180a-bboth include a yaw proof mass170a-b, yaw sense springs171a-dand the electrostatic transducers522a-b.

Rotating structure161is coupled to the anchor141via springs115a-d. Rotating structure161is connected to the drive systems110a-bvia coupling springs131a-band finally rotating structure supports the yaw proof mass systems180a-bvia springs171a-d. In the drive motion of the single-axis gyroscope300, electrostatic actuators109a-bdrives the proof masses130aand130banti-phase in Y direction. Anti-phase motion of drive masses130a-bresult in rotation of rotating structure161around Z-axis which is detected by the drive-sense combs106aand106b. As a result of the Z axis rotation of rotating structure161, yaw proof masses170a-btranslate anti-phase in the X direction since they are attached to rotating structure161through springs171a-d. Springs171a-dare very stiff in the X direction so that they don't deflect during the drive motion.

While the yaw proof masses are driven in X direction, an angular velocity about a yaw input axis in the Z direction that is normal to the substrate101will cause Coriolis forces to act on yaw proof masses170a-bin the Y-direction. The Coriolis forces cause the proof masses170a-bto translate anti-phase in Y direction. The amplitude of the rotation of the proof masses is proportional to the angular velocity about the yaw-input axis. The capacitive in-plane sense electrodes522aand522b, which are attached to the substrate101via anchors, are used to detect the Y direction translation of the proof masses170a-b. This translation provides a measure of the angular velocity about the yaw-input axis.

InFIG. 3, springs115a-dare configured such a way that the out of plane rotation and translation of rotating structure161is minimized. As a result, single-axis gyroscope300is not responsive to Coriolis forces around pitch and roll-input axes. However, for different embodiments, the spring configuration can be adjusted to detect the Coriolis response due to pitch and roll axes inputs.

The drive systems110aand110bare decoupled from the yaw proof masses170aand170bby using a similar approach given inFIG. 1A. Consequently, the benefits of decoupling the drive system from the sensing proof mass mentioned in the explanation ofFIGS. 1A and 1Bwill apply equally to the single-axis gyroscope300.

FIG. 4illustrates a fifth embodiment of a single axis gyroscope400in accordance with the present invention. In the gyroscope400, a guided mass system401is disposed in an X-Y plane parallel to a substrate101. The guided mass system401includes guiding arms104aand104bthat are flexibly coupled via springs108aand108bto the substrate101via the anchoring points142aand142b, respectively. The two guiding arms104aand104bare flexibly coupled to the roll proof-masses200a-bvia springs103a-d.

The roll proof-masses200a-b, guiding arms104aand104b, anchoring points142a-b, and springs103a-d,108a-bform a planar four-bar linkage. Each spring103a-dand108a-bis compliant in-plane about an axis in the Z-direction so that each guiding arm104aand104bcan rotate in-plane while the proof-masses200a-btranslates anti-phase in an X-direction.

The springs108aand108bare compliant about a first roll-sense axis in the X-direction so that the guiding arms104aand104bcan rotate out-of-plane. The springs103a-dare stiff in the Z-direction, whereby out-of-plane rotation of the guiding arms104aand104bcauses the roll proof-masses200a-bto move anti-phase out-of-plane.

Drive systems110aand110bare similar to the drive system110described with respect toFIG. 3. Drive systems110a-bboth include anchors120a-b, drive springs105a-d, drive masses130a-b, drive-sense combs106aand106band electrostatic actuators109a-band they are coupled to guiding arms104aand104bvia coupling springs131aand131b.

The guided mass system401can be driven at a drive frequency by a single drive circuit coupled to the actuators109aand109b. The drive frequency can be a resonant frequency of the single-axis gyroscope400. When the drive masses130a-bare driven anti-phase in the Y direction with the electrostatic force applied by the actuators109a-b, the guiding arms104aand104brotate in-plane and the roll proof-masses200a-btranslates in-plane anti-phase in the X-direction which is detected by the drive-sense combs106aand106b.

Angular velocity about a roll-input axis in the Y-direction that is in the plane of the substrate and orthogonal to the X-direction will cause Coriolis forces to act on the roll proof-masses200a-bin the Z-direction. The Coriolis forces cause the guided mass system401to rotate out-of-plane about the first roll-sense axis which is parallel to the X-direction. When the guided mass system401rotates out-of-plane, the guiding arms104aand104band the roll proof-masses200a-brotate out-of-plane about the first roll-sense axis.

The amplitude of the rotation of the guided mass system401is proportional to the angular velocity about the roll-input axis. Transducers201a-bunder the roll proof-masses200a-bare used to detect the rotation of the guided mass system401about the roll-sense axis. This rotation provides a measure of the angular velocity about the roll-input axis.

FIG. 5illustrates a sixth embodiment of a single axis gyroscope500in accordance with the present invention In the gyroscope500, a guided mass system501comprises guided proof masses200a-b, guiding arm104a, and pitch proof mass210. Single axis gyroscope further comprises drive system110, which is similar to the drive system given inFIG. 1A. Drive system110is coupled to the guided mass system501via coupling spring131. Guiding arm104ais connected to substrate101via spring108athrough anchor142a. Guided proof masses200aand200bare coupled to guiding arm104avia springs103aand103c, respectively. Furthermore, guided proof masses200a-bare coupled to the substrate via springs119a-bthrough anchor143.

The pitch proof-mass210is flexibly connected to two guided proof-masses200aand200bvia springs210aand210b, respectively. Springs210aand210bare torsionally compliant such that pitch proof-mass210can rotate out-of-plane about a pitch sense axis in the Y-direction. During the drive motion of single axis gyroscope500, drive mass130is driven in Y direction by actuator109. The Y direction motion is transferred to the guided mass system through coupling spring131and results in rotation of guiding arm104aabout an axis that is parallel to the Z direction. The in-plane rotation of guided arm104acauses anti-phase translation of guided proof masses200a-bin the X direction. Springs210aand210bare compliant in-plane such that when the guided proof-masses200aand200bare driven anti-phase in the X-direction; the pitch proof-mass210rotate in-plane about an axis in the Z-direction.

Angular velocity about the pitch-input axis will cause Coriolis forces to act on the pitch proof-mass210resulting in a torque that rotates the pitch proof-mass210about the pitch-sense axis. The amplitude of the rotation of the pitch proof-mass210is proportional to the angular velocity about the pitch-input axis. Transducers211aand211bare disposed on opposite sides along the X-direction under the pitch proof-mass210and detect the rotation of the pitch proof-mass about the pitch-sense axis. This rotation provides a measure of the angular velocity about the pitch-input axis.

FIG. 6illustrates a seventh embodiment of a single axis gyroscope600in accordance with the present invention. Single axis gyroscope600includes a guided mass system601coupled to two yaw proof masses170aand170band a drive system110.

Drive system110is coupled to the guided mass system601via coupling spring131. Guiding arm104ais connected to substrate101via spring108athrough anchor142a. Guided proof masses200aand200bare coupled to guiding arm104avia springs103aand103c, respectively. Furthermore, guided proof masses200a-bare coupled to the substrate via springs119a-bthrough anchor143.

The yaw proof-masses170aand170bare flexibly connected to guided proof masses200aand200bvia springs171a-band171c-drespectively. Springs171a-dare compliant in Y direction such that yaw proof-masses170aand170bcan translate along an axis parallel to the Y direction. During the drive motion of single axis gyroscope600, drive mass130is driven in Y direction by actuator109. The Y direction motion is transferred to the guided mass system through coupling spring131and results in rotation of guiding arm104aabout an axis that is parallel to the Z direction. The in-plane rotation of guided arm104acauses anti-phase translation of guided proof masses200a-bin the X direction. Springs171a-dare axially stiff in the X-direction such that when the guided proof-masses200aand200bare driven anti-phase in the X-direction, the yaw proof-masses170aand170balso translate anti-phase in the X-direction.

Angular velocity about the yaw-input axis will cause Coriolis forces to act on the yaw proof-masses170aand170bresulting in motion of the yaw proof-masses170a-banti-phase along the Y-direction. The amplitude of the motion of the yaw proof masses along the Y-direction is proportional to the angular velocity. Transducers522aand522bare used to sense the motion of the respective yaw proof masses170aand170balong the Y-direction.

FIG. 7illustrates a single axis shear mode gyroscope700in accordance with the present invention. Gyroscope700includes shear masses200aand200bwhich are coupled to a substrate101via spring elements119a-band119c-dthrough anchors143aand143b. Drive systems110a-bare connected to the shear proof masses200aand200bvia coupling springs131aand131b, respectively. The pitch proof-mass210is flexibly connected to two shear masses200aand200bvia springs210aand210b. Springs210aand210bare torsionally compliant such that pitch proof-mass210can rotate out-of-plane about a pitch sense axis in the Y-direction.

Each drive system110aand110bofFIG. 7includes a drive mass130a-bwhich are coupled to the substrate via drive springs105a-band105c-dthrough the anchors120a-b. In the drive motion of single axis shear mode gyroscope700, the drive masses130a-bare driven anti-phase in the X direction by the actuators109aand109b. X direction motion of the drive masses130a-bis transferred to the shear masses200a-bvia the coupling springs131a-b. As a result, the shear masses200a-bare driven anti-phase in the X-direction. Springs210aand210bare compliant in-plane such that when the shear masses200aand200bare driven anti-phase in the X-direction; the pitch proof-mass210rotate in-plane about an axis in the Z-direction.

Drive motion of the shear masses200aand200bis referred to hereinafter as shear mode drive motion. Shear mode drive motion can be generalized by defining a specific motion between the two shear masses200aand200band their coupling relationship. In the shear mode drive motion, the two shear masses200aand200bare coupled with a spring or spring-mass system, and the shear masses200aand200btranslate anti-phase along a direction that is perpendicular to a line that is connecting their geometric center.

Angular velocity about the pitch-input axis will cause Coriolis forces to act on the pitch proof-mass210resulting in a torque that rotates the pitch proof-mass210about the pitch-sense axis. The amplitude of the rotation of the pitch proof-mass210is proportional to the angular velocity about the pitch-input axis. Transducers211aand211bare disposed on opposite sides along the X-direction under the pitch proof-mass210and detect the rotation of the pitch proof-mass about the pitch-sense axis. This rotation provides a measure of the angular velocity about the pitch-input axis.

FIG. 8illustrates a first embodiment of a tri-axis gyroscope800in accordance with the present invention. The gyroscope800includes two guided mass systems801and802coupled together by a coupling spring302which connects roll proof-masses200band200c. Guided mass system801comprises guided roll proof-masses200a-b, guiding arms104a-b, and yaw proof-masses170a-b. The yaw proof-masses170aand170bare flexibly connected to the roll proof-masses200aand200bvia springs171a-band171c-drespectively. Guided mass system802comprises guided roll proof-masses200c-d, guiding arms104c-d, and a pitch proof mass210. The pitch proof-mass210is flexibly connected to two guided proof-masses200aand200bvia springs210aand210b, respectively. Springs210aand210bare torsionally compliant such that pitch proof-mass210can rotate out-of-plane about a pitch sense axis in the Y-direction. Drive systems110aand110bare coupled to the guided mass system801through guiding arms104aand104bvia coupling springs131aand131b. In different embodiments of tri-axis gyroscope800, drive systems110a-bcan also be coupled to guided mass system802.

Tri-axis gyroscope800is driven at a drive frequency by a single drive circuit (not shown) coupled to the actuators109a-b. The drive masses130a-bare vibrated anti-phase in the Y direction with the electrostatic force applied by the actuators109a-b. Motion of the drive masses130a-btransferred to the guiding arms104aand104bthrough the coupling springs131aand131b. Guiding arms104aand104brotate in-plane around an axis that is parallel to the Z direction due to the applied torque which is a result of the motion of the drive masses130a-b. As a result of the in-plane rotation of guiding arms104aand104b, the roll proof-masses200a-btranslates in-plane anti-phase in the X-direction. Springs171a-dare axially stiff in the X-direction such that when the roll proof-masses200aand200bare driven anti-phase in the X-direction, the yaw proof-masses170aand170balso translate anti-phase in the X-direction.

The coupling spring302is stiff in the X-direction such that roll proof-masses200band200cmove together in the X-direction. The roll proof-masses200aand200dmove in opposite direction of roll proof-masses200band200c. Springs210aand210bare compliant in-plane such that when the roll proof-masses200c-dare driven, the pitch proof-mass210rotate in-plane about an axis parallel to the Z-direction.

Angular velocity about the pitch-input axis will cause Coriolis forces to act on the pitch proof-mass210resulting in a torque that rotates the pitch proof-mass210about the pitch-sense axis. The amplitude of the rotation of the pitch proof-mass210is proportional to the angular velocity about the pitch-input axis. Transducers211aand211bare disposed on opposite sides along the X-direction under the pitch proof-mass210and detect the rotation of the pitch proof-mass about the pitch-sense axis. This rotation provides a measure of the angular velocity about the pitch-input axis.

Angular velocity about the roll-input axis causes Coriolis forces to act on the roll proof-masses200a-din the positive and negative Z-direction. The coupling spring302is torsionally compliant about an axis in the X-direction so that the guided mass systems801and802can rotate anti-phase out-of-plane about the first and second roll-sense axes. The coupling spring302is stiff in the Z-direction which prevents the guided mass systems801and802from rotating in-phase out-of-plane. Transducers201a-cunder the roll proof masses200a-dare used to detect the rotations of the guided mass systems801and802about the first and second roll-sense axes.

Angular velocity about the yaw-input axis will cause Coriolis forces to act on the yaw proof-masses170aand170bresulting in motion of the yaw proof-masses170aand170banti-phase along the Y-direction. The amplitude of the motion of the yaw proof-masses along the Y-direction is proportional to the angular velocity. Transducers522aand522bare used to sense the motion of the respective yaw proof masses170aand170balong the Y-direction.

FIG. 9illustrates a second embodiment of a tri-axis gyroscope900in accordance with the present invention. Tri-axis gyroscope900comprises three guided mass systems901,902,903and two drive mass systems110a-b. Guided mass systems901and903are coupled to guided mass system902by coupling springs302aand302b. And drive mass systems110aand110bare coupled to the guided mass system902via coupling springs131aand131b.

The guided mass systems901,902and903are arranged so that the roll proof-masses200a-dall move in the X-direction, the pitch proof-mass210rotates about an axis in the Z-direction, and the yaw proof-masses170aand170bmove anti-phase in the X-direction. The guided mass system901rotates out-of-plane about a first roll-sense axis. The guided mass system902rotates out-of-plane about a second roll-sense axis parallel to the first roll-sense axis. The guided mass system903rotates out-of-plane about a third roll-sense axis parallel to the first and second roll-sense axes.

The first coupling spring302ais connected to roll proof-masses200band200c. The coupling spring302ais stiff in the X-direction such that roll proof-mass200band200cmove together in the X-direction. The second coupling spring302bis connected to roll proof-masses200aand200d. The coupling spring302bis stiff in the X-direction such that roll proof-mass200aand200dmove together in the X-direction. In this way the guided mass systems901,902, and903are driven together at a drive frequency by a single drive circuit coupled to the actuators109a-b. During the drive motion, drive masses130a-bare vibrated anti-phase in the Y direction with the electrostatic force applied by the actuators109a-b. Motion of the drive masses130a-btransferred to the guiding arms104aand104bthrough the coupling springs131aand131b, and the guiding arms104a-brotate in-plane around an axis that is parallel to the Z direction. As a result of the in-plane rotation of guiding arms104aand104b, the roll proof-mass pair200band200cand roll proof-mass pair200aand200dtranslate anti-phase in-plane in the X-direction which is detected by the drive-sense combs106a,106b,106c, and106d.

Moreover, during the drive motion, the guided mass systems901,902and903are arranged so that when the roll proof-masses102a-dall move in the X-direction, the pitch proof-mass210rotates about an axis in the Z-direction, and the yaw proof-masses170aand170bmove anti-phase in the X-direction.

The coupling spring302ais torsionally compliant about an axis in the X-direction so that the guided mass systems901and902can rotate out-of-plane about the first and second roll-sense axes anti-phase. The coupling spring302aprevents the symmetric guided mass systems901and902from rotating out-of-plane in-phase.

The coupling spring302bis also torsionally compliant about an axis in the X-direction so that the guided mass systems902and903can rotate out-of-plane about the second and third roll-sense axes anti-phase. The coupling spring302bprevents the symmetric guided mass systems902and903from rotating out-of-plane in-phase.

Angular velocity about the pitch-input axis will cause Coriolis forces to act on the pitch proof-mass210resulting in a torque that rotates the pitch proof-mass210about the pitch-sense axis. The amplitude of the rotation of the pitch proof-mass210is proportional to the angular velocity about the pitch-input axis. Transducers211aand211bare disposed on opposite sides along the X-direction under the pitch proof-mass210and detect the rotation of the pitch proof-mass about the pitch-sense axis. The rotation provides a measure of the angular velocity about the pitch-input axis.

Angular velocity about the roll-input axis will cause Coriolis forces to act on the roll proof-masses200band200cin a Z-direction and on roll proof-masses200aand200din the opposite Z-direction. The Coriolis forces cause the guided mass systems901,902, and903to rotate out-of-plane about the first, second, and third roll-sense axis respectively. Transducer201aunder the roll proof masses200band102cand transducer201aunder the roll proof masses200aand200dare used to detect the rotation of the guided mass systems901,902and903. This rotation provides a measure of the angular velocity about the roll-input axis.

Angular velocity about the yaw-input axis will cause Coriolis forces to act on the yaw proof-masses170aand170bresulting in motion of the yaw proof-masses170aand170banti-phase along the Y-direction. The amplitude of the motion of the yaw proof-masses along the Y-direction is proportional to the angular velocity. Transducers522aand522bare used to sense the motion of the respective yaw proof masses170aand170balong the Y-direction.

CONCLUSION

In all of the above embodiments of the gyroscope, the drive mass is separated from the rotating proof mass and the electrostatic actuators are attached to the drive mass. In so doing, the effect of the non-idealities of the electrostatic actuator on the rotating proof mass is minimized thereby enhancing the overall sensitivity of the gyroscope.