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

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. <CIT> discloses a monolithic triaxial gyro that includes a mass block and a drive comb group. The mass block includes main masses and a coupling mass coupled with the main masses. The main masses are positioned on opposite sides of the coupling mass and are symmetrical with each other along a Y-axis. A first electrode group is included within an orthographic projection of the mass block, a second electrode group is included within an orthographic projection of the coupling mass and a third electrode group includes a group of immovable slender flat plates and a group of movable slender flat plates. The drive comb group is connected to the main masses for driving movement of the main masses when signals are inputted into the drive comb group. <CIT> discloses a gyroscope self-test method by rotating a proof mass at a high frequency. <CIT> discloses a gyroscope for detecting rotation about a gyro input axis, having a support structure, at least one mass flexibly coupled to the support structure such that it is capable of motion in two directions along a drive axis. <CIT> discloses a microelectromechanical integrated sensor structure having a rotary driving motion. <CIT> discloses a microelectromechanical structure, in particular a biaxial or triaxial gyroscope, provided with a rotary driving movement.

It is therefore the object of the present invention to provide an improved angular rate sensor comprising a sense system and a drive system. This object is solved by the subject matter of claim <NUM>. A preferred embodiment is defined by dependent claim <NUM>.

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.

The present invention relates generally to angular velocity sensors and more particularly relates to angular velocity sensors that include guided mass systems. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the preferred embodiments and the generic principles and features described herein will be readily apparent to those skilled in the art. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the is appended claims.

<FIG> illustrates a first example of a single axis gyroscope 100a that does not correspond to the claimed invention. The single axis gyroscope is disposed in an X-Y plane parallel to a substrate <NUM> and comprises a drive system <NUM>, a sense system 159a and a coupling element <NUM>. The drive system <NUM> includes a drive mass <NUM>, an electrostatic actuator <NUM>, two drive springs 105a-b, an anchor <NUM> and two drive-sense electrodes 106a-b. The drive springs 105a-b and the anchor <NUM> act as a suspension system for the drive mass. The sense system 159a comprises a rotating proof mass 150a, a pivot spring <NUM>, an anchor <NUM> and two capacitive sense electrodes 151a and 151b. Finally, the drive system <NUM> and the sense system 159a are coupled by a coupling spring <NUM>. In an embodiment, the suspension system is stiffer than the coupling spring <NUM> while the drive mass <NUM> is rotating out of plane.

The drive mass <NUM> is coupled to the substrate through spring elements 105a-b and the anchor <NUM>. In the drive operation of the single axis gyroscope 100a, electrostatic forces are applied to the drive mass <NUM> via the electrostatic actuator <NUM>, and the motion of drive mass <NUM> in Y direction is detected by electrostatic transducers 106a and 106b that are called drive-sense electrodes. The detected drive motion can be transferred to circuitry to be used to control the mechanical amplitude of drive mass <NUM> in 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. For example, the actuators or transducers could be piezoelectric, thermal or electromagnetic or the like.

The drive mass <NUM> is driven in the Y direction by the electrostatic actuator <NUM> at a certain frequency, which is referred to as a drive frequency. While drive mass <NUM> is driven in the Y direction, a moment around the Z-axis and a Y-direction force are applied to the rotating proof mass 150a through the coupling spring <NUM>. If the pivot spring <NUM> is very stiff in the Y direction, the rotating proof mass 150a rotates around an axis that is parallel to the Z-axis due to the applied moment. The described motion of the drive mass <NUM> and rotating proof mass 150a is referred to as a drive motion.

When the gyroscope 100a is subject to an angular velocity about a roll-input axis in the Y-direction that is in the plane of the substrate <NUM> and orthogonal to the X-direction will cause Coriolis forces to act on the rotating proof mass 150a in the Z-direction. The Coriolis forces cause the rotating proof mass 150a to 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 mass 150a is proportional to the angular velocity about the roll-input axis and also mechanical drive amplitude of the rotating proof mass 150a. The capacitive sense electrodes 151a and 151b, which are placed on the substrate <NUM> under the rotating proof mass 150a, are used to detect the rotation of the rotating proof mass 150a about the roll-sense axis. This rotation provides a measure of the angular velocity about the roll-input axis. Although the capacitive electrodes 151a and 151b are given as transducers to detect the rotation of the rotating proof mass 150a around the roll-sense axis, various types of transducers could be utilized. For example, the capacitive electrodes 151a-b could be also piezoelectric or optical or the like.

As it is given in <FIG> and <FIG>, the drive mass <NUM> is separated from the rotating proof mass 150a and the electrostatic actuators <NUM> are attached to the drive mass <NUM>. A benefit of this approach is to eliminate the effect of the non-idealities of the electrostatic actuator <NUM> on the rotating proof mass 150a. 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 mass 150a around its sensitive axis. The unwanted rotation of the rotating proof mass 150a around its sensitive axis would lead to erroneous motion which can be detected by the capacitive sense electrodes 151a-b resulting in an error in the measurement of angular velocity.

On the other hand, in <FIG> and <FIG>, drive mass <NUM> is coupled to the anchor <NUM> via springs 105a-b which are very stiff in Z direction. As a result, the motion of drive mass <NUM> due to the non-ideal out-of plane electrostatic forces by actuator <NUM> is minimized. Consequently, the non-ideal forces are not transferred to the proof mass 150a, and measurement errors are reduced.

In <FIG>, the coupling spring <NUM>, which is used to transfer the linear Y direction motion of the drive mass <NUM> to the rotation of the proof mass 150a, 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 spring <NUM> in example 100a can be an option to satisfy those compliance conditions.

If the coupling spring <NUM> is made very stiff in Y-direction, but act as a pivot for rotation about z-axis, the whole single axis gyroscope 100a would act as a single Degree of Freedom (DOF) mechanical system in the drive motion. The Y-direction motion of drive mass <NUM> is converted to in-plane rotation of the proof mass 150a around an axis parallel to the Z direction. The amount of rotation of proof mass <NUM> depends on the ratio of the length of the coupling spring to the radius of rotation of the proof mass 150a with respect to the center of its rotation. The Y-direction motion is either amplified or attenuated depending on the ratio. Moreover, the drive-sense electrodes 106a-b can be placed on the drive mass <NUM> without effecting the closed loop drive operation.

<FIG> illustrates a second embodiment of a single axis gyroscope in accordance with the present invention. In the embodiment shown in <FIG>, the coupling spring <NUM> is compliant in the Y-direction and can be designed so that single axis gyroscope 100b acts as a two DOF system in the drive motion. In that configuration, the sense system 159b can be designed as a vibration absorber of the drive mass <NUM>. As a result, small motion on drive mass <NUM> can be amplified to get bigger motion on the sense mass 150a. For a vibration absorber configuration, it is necessary that drive-sense electrodes 106a-b to be connected to the rotating proof-mass 150a as it is shown in <FIG>. The connection is necessary to allow the rotational motion of rotating proof mass 150a at a certain mechanical amplitude around the Z axis (the main component of the drive motion) to maximize the sensitivity of the gyroscope 100b.

The small motion on the drive mass <NUM> is beneficial for area optimization. If the drive mass <NUM> has 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 gyroscope 100b in more detail refer now to <FIG> and <FIG>. <FIG> is a simple block diagram of the gyroscope 100b, the reference numerals which conform to those of <FIG>. It is desirable in the gyroscope 100b that the drive mass <NUM> moves less than the sense mass 150a. The minimization of motion of <NUM> is accomplished by tuning the coupling spring kc (<NUM>) such that it is at least an order of magnitude more flexible than the springs kd (105a/105b) and ks (<NUM>).

To explain the tuning of kc spring in more detail, bode plots of the transfer functions Xd/Fd and Xs/Fd are shown in <FIG> where Xd is the movement of the drive mass <NUM> in a first direction, Xs is the movement the sense mass 150a in a second direction and Fd is the force caused by the actuator <NUM> on the drive mass <NUM>. In <FIG>, 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 in <FIG>, an expansion of a specific region has been shown. Based on the <NUM>-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 <NUM>-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> illustrates a third embodiment of a single axis gyroscope <NUM> in accordance with the present invention. In this embodiment, the sense system <NUM> has some differences compared to the sense system 159a which is shown in <FIG>. The sense system <NUM> comprises a circular proof mass 150b, instead of a rectangular proof mass 150a given in <FIG>. Moreover, the proof mass 150b is coupled to the substrate via two pivot springs 115a and 115b and the anchor <NUM>. The drive system <NUM> is similar to the embodiment given in <FIG>. Similar to the single axis gyroscopes shown in <FIG> and <FIG>, the single axis gyroscope <NUM> is driven via electrostatic actuator <NUM> attached to the drive mass <NUM>.

When the drive mass <NUM> is driven in Y direction, the proof mass 150b rotates around Z axis. The amplitude of the drive motion of the proof mass 150b depends on the drive mass <NUM> motion and the coupling spring <NUM> stiffness as it was explained previously. The amplitude of drive motion of the proof mass 150b is detected by the drive sense electrodes 106a and 106b.

An angular velocity about a roll-input axis in the Y-direction that is in the plane of the substrate <NUM> and orthogonal to the X-direction will cause Coriolis forces to act on the proof mass 150b in the Z-direction. The Coriolis forces cause the proof mass 150b to rotate out-of-plane about the roll-sense axis which is parallel to the X-direction. The amplitude of the rotation of the proof mass 150b is proportional to the angular velocity about the roll-input axis. The capacitive sense electrodes 151a and 151b, which are placed on the substrate <NUM> under the proof mass 150b, are used to detect the rotation of the proof mass 150b about the roll-sense axis. This rotation provides a measure of the angular velocity about the roll-input axis.

<FIG> illustrates a fourth embodiment of a single-axis gyroscope <NUM> configuration in accordance with the present invention. The gyroscope configuration <NUM> includes two drive systems 110a and 110b, two coupling springs 131a and 131b, a rotating structure <NUM> and two yaw proof mass systems 180a and 180b. Drive systems 110a and 110b are similar to the drive system <NUM> given in <FIG>, <FIG> and <FIG>. Drive systems 110a-b both include anchors 120a-b, drive springs 105a-d, drive masses 130a-b, drive-sense combs 106a and 106b and electrostatic actuators 109a-b. Yaw proof mass systems 180a-b both include a yaw proof mass 170a-b, yaw sense springs 171a-d and the electrostatic transducers 522a-b.

Rotating structure <NUM> is coupled to the anchor <NUM> via springs 115a-d. Rotating structure <NUM> is connected to the drive systems 110a-b via coupling springs 131a-b and finally rotating structure supports the yaw proof mass systems 180a-b via springs 171a-d. In the drive motion of the single-axis gyroscope <NUM>, electrostatic actuators 109a-b drives the proof masses 130a and 130b anti-phase in Y direction. Anti-phase motion of drive masses 130a-b result in rotation of rotating structure <NUM> around Z-axis which is detected by the drive-sense combs 106a and 106b. As a result of the Z axis rotation of rotating structure <NUM>, yaw proof masses 170a-b translate anti-phase in the X direction since they are attached to rotating structure <NUM> through springs 171a-d. Springs 171a-d are 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 substrate <NUM> will cause Coriolis forces to act on yaw proof masses 170a-b in the Y-direction. The Coriolis forces cause the proof masses 170a-b to 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 electrodes 522a and 522b, which are attached to the substrate <NUM> via anchors, are used to detect the Y direction translation of the proof masses 170a-b. This translation provides a measure of the angular velocity about the yaw-input axis.

In <FIG>, springs 115a-d are configured such a way that the out of plane rotation and translation of rotating structure <NUM> is minimized. As a result, single-axis gyroscope <NUM> is 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 systems 110a and 110b are decoupled from the yaw proof masses 170a and 170b by using a similar approach given in <FIG>. Consequently, the benefits of decoupling the drive system from the sensing proof mass mentioned in the explanation of <FIG> and <FIG> will apply equally to the single-axis gyroscope <NUM>.

<FIG> illustrates a fifth embodiment of a single axis gyroscope <NUM> in accordance with the present invention. In the gyroscope <NUM>, a guided mass system <NUM> is disposed in an X-Y plane parallel to a substrate <NUM>. The guided mass system <NUM> includes guiding arms 104a and 104b that are flexibly coupled via springs 108a and 108b to the substrate <NUM> via the anchoring points 142a and 142b, respectively. The two guiding arms 104a and 104b are flexibly coupled to the roll proof-masses 200a-b via springs 103a-d.

The roll proof-masses 200a-b, guiding arms 104a and 104b, anchoring points 142a-b, and springs 103a-d, 108a-b form a planar four-bar linkage. Each spring 103a-d and 108a-b is compliant in-plane about an axis in the Z-direction so that each guiding arm 104a and 104b can rotate in-plane while the proof-masses 200a-b translates anti-phase in an X-direction.

The springs 108a and 108b are compliant about a first roll-sense axis in the X-direction so that the guiding arms 104a and 104b can rotate out-of-plane. The springs 103a-d are stiff in the Z-direction, whereby out-of-plane rotation of the guiding arms 104a and 104b causes the roll proof-masses 200a-b to move anti-phase out-of-plane.

Drive systems 110a and 110b are similar to the drive system <NUM> described with respect to <FIG>. Drive systems 110a-b both include anchors 120a-b, drive springs 105a-d, drive masses 130a-b, drive-sense combs 106a and 106b and electrostatic actuators 109a-b and they are coupled to guiding arms 104a and 104b via coupling springs 131a and 131b.

The guided mass system <NUM> can be driven at a drive frequency by a single drive circuit coupled to the actuators 109a and 109b. The drive frequency can be a resonant frequency of the single-axis gyroscope <NUM>. When the drive masses 130a-b are driven anti-phase in the Y direction with the electrostatic force applied by the actuators 109a-b, the guiding arms 104a and 104b rotate in-plane and the roll proof-masses 200a-b translates in-plane anti-phase in the X-direction which is detected by the drive-sense combs 106a and 106b.

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-masses 200a-b in the Z-direction. The Coriolis forces cause the guided mass system <NUM> to rotate out-of-plane about the first roll-sense axis which is parallel to the X-direction. When the guided mass system 401rotates out-of-plane, the guiding arms 104a and 104b and the roll proof-masses 200a-b rotate out-of-plane about the first roll-sense axis.

The amplitude of the rotation of the guided mass system <NUM> is proportional to the angular velocity about the roll-input axis. Transducers 201a -b under the roll proof-masses 200a-b are used to detect the rotation of the guided mass system <NUM> about the roll-sense axis. This rotation provides a measure of the angular velocity about the roll-input axis.

<FIG> illustrates a sixth example of a single axis gyroscope <NUM> that does not correspond to the claimed invention. In the gyroscope <NUM>, a guided mass system <NUM> comprises guided proof masses 200a-b, guiding arm 104a, and pitch proof mass <NUM>. Single axis gyroscope further comprises drive system <NUM>, which is similar to the drive system given in <FIG>. Drive system <NUM> is coupled to the guided mass system <NUM> via coupling spring <NUM>. Guiding arm 104a is connected to substrate <NUM> via spring 108a through anchor 142a. Guided proof masses 200a and 200b are coupled to guiding arm 104a via springs 103a and 103c, respectively. Furthermore, guided proof masses 200a-b are coupled to the substrate via springs 119a-b through anchor <NUM>.

The pitch proof-mass <NUM> is flexibly connected to two guided proof-masses 200a and 200b via springs 210a and 210b, respectively. Springs 210a and 210b are torsionally compliant such that pitch proof-mass <NUM> can rotate out-of-plane about a pitch sense axis in the Y-direction. During the drive motion of single axis gyroscope <NUM>, drive mass <NUM> is driven in Y direction by actuator <NUM>. The Y direction motion is transferred to the guided mass system through coupling spring <NUM> and results in rotation of guiding arm 104a about an axis that is parallel to the Z direction. The in-plane rotation of guided arm 104a causes anti-phase translation of guided proof masses 200a-b in the X direction. Springs 210a and 210b are compliant in-plane such that when the guided proof-masses 200a and 200b are driven anti-phase in the X-direction; the pitch proof-mass <NUM> rotate 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-mass <NUM> resulting in a torque that rotates the pitch proof-mass <NUM> about the pitch-sense axis. The amplitude of the rotation of the pitch proof-mass <NUM> is proportional to the angular velocity about the pitch-input axis. Transducers 211a and 211b are disposed on opposite sides along the X-direction under the pitch proof-mass <NUM> and 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> illustrates a seventh example of a single axis gyroscope <NUM> that does not correspond to the claimed invention. Single axis gyroscope <NUM> includes a guided mass system <NUM> coupled to two yaw proof masses 170a and 170b and a drive system <NUM>.

Drive system <NUM> is coupled to the guided mass system <NUM> via coupling spring <NUM>. Guiding arm 104a is connected to substrate <NUM> via spring 108a through anchor 142a. Guided proof masses 200a and 200b are coupled to guiding arm 104a via springs 103a and 103c, respectively. Furthermore, guided proof masses 200a-b are coupled to the substrate via springs 119a-b through anchor <NUM>.

The yaw proof-masses 170a and 170b are flexibly connected to guided proof masses 200a and 200b via springs 171a-b and 171c-d respectively. Springs 171a-d are compliant in Y direction such that yaw proof-masses 170a and 170b can translate along an axis parallel to the Y direction. During the drive motion of single axis gyroscope <NUM>, drive mass <NUM> is driven in Y direction by actuator <NUM>. The Y direction motion is transferred to the guided mass system through coupling spring <NUM> and results in rotation of guiding arm 104a about an axis that is parallel to the Z direction. The in-plane rotation of guided arm 104a causes anti-phase translation of guided proof masses 200a-b in the X direction. Springs 171a-d are axially stiff in the X-direction such that when the guided proof-masses 200a and 200b are driven anti-phase in the X-direction, the yaw proof-masses 170a and 170b also translate anti-phase in the X-direction.

Angular velocity about the yaw-input axis will cause Coriolis forces to act on the yaw proof-masses 170a and 170b resulting in motion of the yaw proof-masses 170a-b anti-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. Transducers 522a and 522b are used to sense the motion of the respective yaw proof masses 170a and 170b along the Y-direction.

<FIG> illustrates a single axis shear mode gyroscope <NUM> that does not correspond to the claimed invention. Gyroscope <NUM> includes shear masses 200a and 200b which are coupled to a substrate <NUM> via spring elements 119a-b and 119c-d through anchors 143a and 143b. Drive systems 110a-b are connected to the shear proof masses 200a and 200b via coupling springs 131a and 131b, respectively. The pitch proof-mass <NUM> is flexibly connected to two shear masses 200a and 200b via springs 210a and 210b. Springs 210a and 210b are torsionally compliant such that pitch proof-mass <NUM> can rotate out-of-plane about a pitch sense axis in the Y-direction.

Each drive system 110a and 110b of <FIG> includes a drive mass 130a-b which are coupled to the substrate via drive springs 105a-b and 105c-d through the anchors 120a-b. In the drive motion of single axis shear mode gyroscope <NUM>, the drive masses 130a-b are driven anti-phase in the X direction by the actuators 109a and 109b. X direction motion of the drive masses 130a-b is transferred to the shear masses 200a-b via the coupling springs 131a-b. As a result, the shear masses 200a-b are driven anti-phase in the X-direction. Springs 210a and 210b are compliant in-plane such that when the shear masses 200a and 200b are driven anti-phase in the X-direction; the pitch proof-mass <NUM> rotate in-plane about an axis in the Z-direction.

Drive motion of the shear masses 200a and 200b is referred to hereinafter as shear mode drive motion. Shear mode drive motion can be generalized by defining a specific motion between the two shear masses 200a and 200b and their coupling relationship. In the shear mode drive motion, the two shear masses 200a and 200b are coupled with a spring or spring-mass system, and the shear masses 200a and 200b translate anti-phase along a direction that is perpendicular to a line that is connecting their geometric center.

<FIG> illustrates a first example of a tri-axis gyroscope <NUM> that does not correspond to the claimed invention. The gyroscope <NUM> includes two guided mass systems <NUM> and <NUM> coupled together by a coupling spring <NUM> which connects roll proof-masses 200b and 200c. Guided mass system <NUM> comprises guided roll proof-masses 200a-b, guiding arms 104a-b, and yaw proof-masses 170a-b. The yaw proof-masses 170a and 170b are flexibly connected to the roll proof-masses 200a and 200b via springs 171a-b and 171c-d respectively. Guided mass system <NUM> comprises guided roll proof-masses 200c-d, guiding arms 104c-d, and a pitch proof mass <NUM>. The pitch proof-mass <NUM> is flexibly connected to two guided proof-masses 200a and 200b via springs 210a and 210b, respectively. Springs 210a and 210b are torsionally compliant such that pitch proof-mass <NUM> can rotate out-of-plane about a pitch sense axis in the Y-direction. Drive systems 110a and 110b are coupled to the guided mass system <NUM> through guiding arms 104a and 104b via coupling springs 131a and 131b. In different embodiments of tri-axis gyroscope <NUM>, drive systems 110a-b can also be coupled to guided mass system <NUM>.

Tri-axis gyroscope <NUM> is driven at a drive frequency by a single drive circuit (not shown) coupled to the actuators 109a-b. The drive masses 130a-b are vibrated anti-phase in the Y direction with the electrostatic force applied by the actuators 109a-b. Motion of the drive masses 130a-b transferred to the guiding arms 104a and 104b through the coupling springs 131a and 131b. Guiding arms 104a and 104b rotate 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 masses 130a-b. As a result of the in-plane rotation of guiding arms 104a and 104b, the roll proof-masses 200a-b translates in-plane anti-phase in the X-direction. Springs 171a-d are axially stiff in the X-direction such that when the roll proof-masses 200a and 200b are driven anti-phase in the X-direction, the yaw proof-masses 170a and 170b also translate anti-phase in the X-direction.

The coupling spring <NUM> is stiff in the X-direction such that roll proof-masses 200b and 200c move together in the X-direction. The roll proof-masses 200a and 200d move in opposite direction of roll proof-masses 200b and 200c. Springs 210a and 210b are compliant in-plane such that when the roll proof-masses 200c-d are driven, the pitch proof-mass <NUM> rotate in-plane about an axis parallel to the Z-direction.

Angular velocity about the roll-input axis causes Coriolis forces to act on the roll proof-masses 200a-d in the positive and negative Z-direction. The coupling spring <NUM> is torsionally compliant about an axis in the X-direction so that the guided mass systems <NUM> and <NUM> can rotate anti-phase out-of-plane about the first and second roll-sense axes. The coupling spring <NUM> is stiff in the Z-direction which prevents the guided mass systems <NUM> and <NUM> from rotating in-phase out-of-plane. Transducers 201a-c under the roll proof masses 200a-d are used to detect the rotations of the guided mass systems <NUM> and <NUM> about the first and second roll-sense axes.

Angular velocity about the yaw-input axis will cause Coriolis forces to act on the yaw proof-masses 170a and 170b resulting in motion of the yaw proof-masses 170a and 170b anti-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. Transducers 522a and 522b are used to sense the motion of the respective yaw proof masses 170a and 170b along the Y-direction.

<FIG> illustrates a second embodiment of a tri-axis gyroscope <NUM> in accordance with the present invention. Tri-axis gyroscope <NUM> comprises three guided mass systems <NUM>, <NUM>, <NUM> and two drive mass systems 110a-b. Guided mass systems <NUM> and <NUM> are coupled to guided mass system <NUM> by coupling springs 302a and 302b. And drive mass systems 110a and 110b are coupled to the guided mass system <NUM> via coupling springs 131a and 131b.

The guided mass systems <NUM>, <NUM> and <NUM> are arranged so that the roll proof-masses 200a-d all move in the X-direction, the pitch proof-mass <NUM> rotates about an axis in the Z-direction, and the yaw proof-masses 170a and 170b move anti-phase in the X-direction. The guided mass system <NUM> rotates out-of-plane about a first roll-sense axis. The guided mass system <NUM> rotates out-of-plane about a second roll-sense axis parallel to the first roll-sense axis. The guided mass system <NUM> rotates out-of-plane about a third roll-sense axis parallel to the first and second roll-sense axes.

The first coupling spring 302a is connected to roll proof-masses 200b and 200c. The coupling spring 302a is stiff in the X-direction such that roll proof-mass 200b and 200c move together in the X-direction. The second coupling spring 302b is connected to roll proof-masses 200a and 200d. The coupling spring 302b is stiff in the X-direction such that roll proof-mass 200a and 200d move together in the X-direction. In this way the guided mass systems <NUM>, <NUM>, and <NUM> are driven together at a drive frequency by a single drive circuit coupled to the actuators 109a-b. During the drive motion, drive masses 130a-b are vibrated anti-phase in the Y direction with the electrostatic force applied by the actuators 109a-b. Motion of the drive masses 130a-b transferred to the guiding arms 104a and 104b through the coupling springs 131a and 131b, and the guiding arms 104a-b rotate in-plane around an axis that is parallel to the Z direction. As a result of the in-plane rotation of guiding arms 104a and 104b, the roll proof-mass pair 200b and 200c and roll proof-mass pair 200a and 200d translate anti-phase in-plane in the X-direction which is detected by the drive-sense combs 106a, 106b, 106c, and 106d.

Moreover, during the drive motion, the guided mass systems <NUM>, <NUM> and <NUM> are arranged so that when the roll proof-masses 102a-d all move in the X-direction, the pitch proof-mass <NUM> rotates about an axis in the Z-direction, and the yaw proof-masses 170a and 170b move anti-phase in the X-direction.

The coupling spring 302a is torsionally compliant about an axis in the X-direction so that the guided mass systems <NUM> and <NUM> can rotate out-of-plane about the first and second roll-sense axes anti-phase. The coupling spring 302a prevents the symmetric guided mass systems <NUM> and <NUM> from rotating out-of-plane in-phase.

The coupling spring 302b is also torsionally compliant about an axis in the X-direction so that the guided mass systems <NUM> and <NUM> can rotate out-of-plane about the second and third roll-sense axes anti-phase. The coupling spring 302b prevents the symmetric guided mass systems <NUM> and <NUM> from rotating out-of-plane in-phase.

Angular velocity about the pitch-input axis will cause Coriolis forces to act on the pitch proof-mass <NUM> resulting in a torque that rotates the pitch proof-mass <NUM> about the pitch-sense axis. The amplitude of the rotation of the pitch proof-mass <NUM> is proportional to the angular velocity about the pitch-input axis. Transducers 211a and 211b are disposed on opposite sides along the X-direction under the pitch proof-mass <NUM> and 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-masses 200b and 200c in a Z-direction and on roll proof-masses 200a and 200d in the opposite Z-direction. The Coriolis forces cause the guided mass systems <NUM>, <NUM>, and <NUM> to rotate out-of-plane about the first, second, and third roll-sense axis respectively. Transducer 201a under the roll proof masses 200b and 102c and transducer 201a under the roll proof masses 200a and 200d are used to detect the rotation of the guided mass systems <NUM>,<NUM> and <NUM>. This rotation provides a measure of the angular velocity about the roll-input axis.

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.

Claim 1:
An angular rate sensor comprising:
a substrate (<NUM>);
a sense system (159a; 159b; <NUM>) comprising:
a rotating structure 150a; 150b; (<NUM>) coupled to the substrate; and
first and second transducers (106a-b; 151a-b) for detecting a rotation of the rotating structure, wherein
the first transducer (106a-b) is responsive to the rotational oscillation of the rotating structure during a drive mode, and
the second transducer which is responsive to angular velocity of the angular rate sensor; and
a drive system (<NUM>; 110a, 110b) comprising:
a drive mass (<NUM>; 130a, 130b) coupled to the substrate; and
an actuator (<NUM>; 109a, 109b) coupled to the drive mass, the actuator driving the drive mass moving in a direction parallel to the substrate in a first direction; and
a flexible element (<NUM>; 131a, 131b) coupling the drive system to the sense system, wherein the actuator in the drive system is coupled to the rotating structure in the sense system via the drive mass for driving the rotating structure into rotational oscillation around a first axis normal to the substrate.