Fully decoupled lateral axis gyroscope with thickness-insensitive Z-axis spring and symmetric teeter totter sensing element
View Patent ↗A micro-electromechanical systems (MEMS) transducer ( 400 ) is adapted to use lateral axis vibration of the drive mass ( 210 ) to generate non-planar oscillations of a coupling mass ( 220 ) in response to Coriolis forces created from in-plane rotation, which in turn generate non-planar motions of a symmetric teeter-totter sense mass ( 230 ) which are detected as a capacitive difference signal by capacitive electrodes ( 403, 404 ) formed on the substrate ( 402 ) below the sense mass ( 230 ).
1. A lateral axis MEMS sensor for measuring rotational motion about a center line axis, comprising:
a substrate;
a pair of electrodes formed on the substrate and symmetrically positioned in relation to a center line axis; and
a symmetric gyro sensor positioned in spaced apart relationship above a surface of said substrate and comprising a drive mass, a coupling mass connected to the drive mass, and a sense mass connected to the coupling mass, such that the sense mass is mechanically decoupled from the drive mass, where the sense mass is adapted for rotational motion relative to the center line axis in response to a Coriolis force applied to the coupling mass, where the rotational motion is detected using the pair of electrodes on the substrate that are disposed beneath the sense mass.
2. The lateral axis MEMS sensor of claim 1 , where the drive mass comprises a pair of drive masses formed in a first layer and symmetrically disposed in relation to the center line axis, where the pair of drive masses are coupled by a first anchor system to the substrate to enable the pair of drive masses to undergo oscillatory linear motion within a plane.
3. The lateral axis MEMS sensor of claim 2 , where the coupling mass comprises a pair of coupling masses formed in the first layer and symmetrically disposed in relation to the center line axis, where the pair of coupling masses are coupled by a first spring system to the pair of drive masses to drive the pair of coupling masses to undergo oscillatory linear motion within the plane and to drive the pair of coupling masses to undergo oscillatory out of the plane motion as a function of the angular rate about the center line axis.
4. The lateral axis MEMS sensor of claim 3 , where the first spring system comprises a plurality of vertical beam torsional springs for connecting the pair of drive masses to the pair of coupling masses, where each vertical beam torsional spring comprises:
a body having a length dimension parallel to the center line axis that is longer than a width dimension in the plane that is orthogonal to the center line axis; and
a plurality of beam connector elements which connect the body between a drive mass and sense mass to effectively limit in-plane movement of the body relative to the drive mass and sense mass while allowing non-planar movement of the body relative to the drive and sense mass.
5. The lateral axis MEMS sensor of claim 4 , where the vertical beam torsional spring comprises of a plurality of short and narrow torsion beams and a wide vertical beam such that the lateral axis MEMS sensor will have resonance frequency which is in-sensitive to the variation of the structural layer thickness.
6. The lateral axis MEMS sensor of claim 3 , where the sense mass is formed in the first layer and symmetrically disposed in relation to the center line axis, where the sense mass is coupled by a second anchor system to the substrate and is coupled by a second spring system to the pair of coupling masses to undergo rotational motion about the center line axis when the pair of coupling masses undergo oscillatory out of the plane motion.
7. The lateral axis MEMS sensor of claim 6 , where the second anchor system comprises a first pivot element attached to the substrate below the center line axis and attached to the sense mass at the center line axis with a third spring system.
8. The lateral axis MEMS sensor of claim 6 , where the second spring system comprises a pair of linkage springs formed in the first layer and disposed on opposite ends of the sense mass for connection, respectively, to the pair of coupling masses.
9. The lateral axis MEMS sensor of claim 1 , where the drive mass is designed to move in an in-plane direction, the coupling mass is designed to move in both an in-plane and out-of-plane directions, and the sense mass is designed to move in an out-of-plane direction.
10. The lateral axis MEMS sensor of claim 9 , where the sense mass is a symmetrical teeter tottering mass which rotates around a pivotal axis to suppress undesirable resonance mode and linear acceleration and/or acoustic interference.
11. A transducer adapted to sense angular rotation about a rotational axis comprising:
a substrate;
a proof mass positioned above a surface of said substrate and adapted for motion relative to the rotational axis;
a pair of coupling masses positioned above the surface of said substrate and connected to each other by a first spring system to enable the pair of coupling masses to undergo opposed oscillatory motion within a plane that is parallel to the surface of the substrate, where the pair of coupling masses are disposed symmetrically in relation to the rotational axis and connected on opposite sides of the proof mass by a second spring system which enables the proof mass to rotate about the rotational axis when the pair of coupling masses undergoes oscillatory out of the plane motion; and
a pair of drive masses positioned above the surface of said substrate and connected to each other by a third spring system to enable the pair of drive masses to undergo oscillatory motion within a plane that is parallel to the surface of the substrate, where the pair of drive masses are disposed symmetrically in relation to the rotational axis and connected to the pair of coupling masses by a fourth spring system to drive the pair of coupling masses into opposed oscillatory motion within a plane that is parallel to the surface of the substrate and to enable the pair of coupling masses to undergo oscillatory out of the plane motion in response to a Coriolis force applied to the pair of coupling masses.
12. The transducer of claim 11 , where the pair of drive masses are coupled by a first anchor system to the substrate to enable the pair of drive masses to undergo opposed oscillatory motion within a plane.
13. The transducer of claim 12 , where the first anchor system comprises:
one or more first anchors for connecting the third spring system to the substrate, and
one or more second anchors for flexibly connecting each drive mass to the substrate to enable the pair of drive masses to undergo oscillatory motion within a plane that is parallel to the surface of the substrate.
14. The transducer of claim 11 , further comprising an anchor system formed on said surface of said substrate, said anchor system pivotally coupling said proof mass to the substrate at said rotational axis to enable said proof mass to rotate about said rotational axis in response to said angular velocity about the rotational axis.
15. The transducer of claim 11 , further comprising a pair of electrodes formed on the surface of said substrate and disposed beneath the proof mass for detecting rotation motion of the proof mass relative to the rotational axis.
16. The transducer of claim 11 , where the fourth spring system comprises a plurality of vertical beam torsional springs for connecting the pair of drive masses to the pair of coupling masses, where each vertical beam torsional spring comprises:
a body having a length dimension parallel to the center line axis that is longer than a width dimension in the plane that is orthogonal to the center line axis; and
a plurality of beam connector elements which connect the body between a drive mass and sense mass to effectively limit in-plane movement of the body relative to the drive mass and sense mass while allowing non-planar movement of the body relative to the drive and sense mass.
17. The transducer of claim 11 , where the proof mass, the pair of coupling masses, and the pair of drive masses are all formed in a single layer.
18. The transducer of claim 11 , where the pair of drive masses is designed to move only in in-plane direction, the pair of coupling masses is designed to move in both in-plane and out-of-plane directions, and the proof mass is designed to move only in out-of-plane direction.
19. The transducer of claim 11 , where the proof mass is a symmetrical teeter tottering mass which rotates around a pivotal axis to suppress undesirable resonance mode.
20. The transducer of claim 11 , where the proof mass is a symmetrical teeter tottering mass which rotates around a pivotal axis to increase resistance to linear acceleration and/or acoustic interference.
21. The transducer of claim 11 , where the fourth spring system comprises a plurality of vertical beam torsional springs, where each vertical beam torsional spring comprises a plurality of short and narrow torsion beams and a wide vertical beam such that the lateral axis MEMS sensor will have resonance frequency which is in-sensitive to the variation of the structural layer thickness.