MEMS GYROSCOPE MAGNETIC SENSITIVITY REDUCTION

• US 20100244819A1
• Filed: 03/15/2010
• Published: 09/30/2010
• Est. Priority Date: 03/30/2009
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Johnson, Burgess R., Pant, Bharat
• Granted Patent: US 8,664,951 B2
• Time in Patent Office: Days
• US Class Current: 324/244
• CPC Class Codes: G01C 19/5726 Signal processing
• CPC Class Codes: G01C 19/574 the devices having two sensing masses in anti-phase motion

Abstract

A tuning fork gyroscope that is insensitive to magnetic field gradients is provided. The tuning fork gyroscope includes a first electrically conducting proof mass and a second electrically conducting proof mass connected through electrically conducting suspensions to anchors attached to one or more insulating substrates, and an electrical-resistance mid-point electrically connected to opposing ends of the first electrically conducting proof mass and to opposing ends of the second electrically conducting proof mass. The tuning fork gyroscope provides an input to a sense charge amplifier. The sense charge amplifier generates an output signal indicative of a rotation of the tuning fork gyroscope. The output signal is independent of a magnetic field gradient.

Claims

1. A tuning fork gyroscope that is insensitive to magnetic field gradients, the tuning fork gyroscope comprising:

a first electrically conducting proof mass and a second electrically conducting proof mass connected through electrically conducting suspensions to anchors attached to one or more insulating substrates; and

an electrical-resistance mid-point electrically connected to opposing ends of the first electrically conducting proof mass and to opposing ends of the second electrically conducting proof mass, the tuning fork gyroscope providing an input to a sense charge amplifier, wherein the sense charge amplifier generates an output signal indicative of a rotation of the tuning fork gyroscope, the output signal being independent of a magnetic field gradient.

2. The tuning fork gyroscope of claim 1, wherein the first electrically conducting proof mass and the second electrically conducting proof mass are capacitively coupled to AC ground and the electrical-resistance mid-point is electrically connected to an input of the sense charge amplifier.

3. The tuning fork gyroscope of claim 1, wherein the anchors include a first mid-point stationary anchor and a second mid-point stationary anchor, and wherein a stationary electrical connection connects the first mid-point stationary anchor and the second mid-point stationary anchor, and wherein the electrical-resistance mid-point is a point on the stationary electrical connection, wherein no voltage, due to the magnetic field gradient, is generated at the electrical-resistance mid-point when the proof masses move in an oscillatory motion with opposing velocities along a motor axis in the presence of the magnetic field gradient.

4. The tuning fork gyroscope of claim 3, wherein the electrically conducting suspensions include:

anchor-suspensions mechanically attached to the anchors and mechanically attached to one of a first suspension bar and a second suspension bar;

proof-mass suspensions mechanically attached to one of the first proof mass and the second proof mass and mechanically attached to one of the first suspension bar and the second suspension bar, the tuning fork gyroscope further comprising;

the one or more insulating substrates; and

the anchors formed on the one or more insulating substrates.

5. The tuning fork gyroscope of claim 4, wherein the anchor suspensions include a first portion of the anchor-suspensions and a second portion of the anchor-suspensions, the tuning fork gyroscope further comprising:

the first suspension bar mechanically attached to the first portion of the anchor-suspensions; and

the second suspension bar mechanically attached to the second portion of the anchor-suspensions, the first and second suspension bars located at opposing ends of the proof masses.

6. The tuning fork gyroscope of claim 5, further comprising:

at least one first proof-mass suspension to mechanically attach a first end of a first proof mass to the first suspension bar;

at least one second proof-mass suspension to mechanically attach a first end of the second proof mass to the first suspension bar;

at least one third proof-mass suspension to mechanically attach a second end of the first proof mass to the second suspension bar; and

at least one fourth proof-mass suspension to mechanically attach a second end of the second proof mass to the second suspension bar.

7. The tuning fork gyroscope of claim 6, further comprising:

a first mid-point suspension to mechanically attach the first mid-point stationary anchor to the first suspension bar, wherein the stationary electrical connection is electrically connected to the first suspension bar; and

a second mid-point suspension to mechanically attach the second mid-point stationary anchor to the second suspension bar, wherein the stationary electrical connection is electrically connected to the second suspension bar, wherein the first electrically conducting proof mass and the second electrically conducting proof mass are suspended over the one or more insulating substrates via the anchor-suspensions, the first and second suspension bars, and the proof-mass suspensions.

8. The tuning fork gyroscope of claim 1, where the first electrically conducting proof mass and the second electrically conducting proof mass are capacitively coupled to one or more sense capacitance electrodes having bias voltages.

9. The tuning fork gyroscope of claim 8, wherein an input of the sense charge amplifier is connected to the one or more sense capacitance electrodes having bias voltages, and wherein the electrical-resistance mid-point is connected to AC ground.

10. The tuning fork gyroscope of claim 1, wherein the gyroscope sensor mechanism includes the first and second electrically conducting proof masses, proof-mass suspensions, a first suspension bar, a second suspension bar, and anchor-suspensions.

11. The tuning fork gyroscope of claim 1, wherein the tuning fork gyroscope is one of an out-of-plane tuning fork gyroscope or an in-plane tuning fork gyroscope.

12. The tuning fork gyroscope of claim 1, wherein the electrical-resistance mid-point is formed from the same conducting material as the first electrically conducting proof mass and the second electrically conducting proof mass.

13. The tuning fork gyroscope of claim 1, wherein the tuning fork gyroscope is a tuning fork micro-electrical-mechanical system (MEMS) gyroscope.

14. The tuning fork gyroscope of claim 1, wherein the electrical-resistance mid-point is formed from a conducting material lithographically patterned on the one or more insulating substrates.

15. A method to reduce bias in an output of a tuning fork gyroscope in the presence of a magnetic field gradient, the method comprising:

suspending two electrically conducting proof masses over at least one insulating substrate; and

electrically connecting an electrical-resistance mid-point to opposing ends of the two electrically conducting proof masses, wherein the electrical resistance of the connections from the opposing ends of the two electrically conducting proof masses are equal at the electrical-resistance mid-point, wherein a sense charge amplifier connected to the tuning fork gyroscope generates an output signal indicative of a rotation of the tuning fork gyroscope, the output signal being independent of the magnetic field gradient.

16. The method of claim 15, the method further comprising:

connecting the electrical-resistance mid-point to an input of the sense charge amplifier; and

connecting a second input of the sense charge amplifier to AC ground.

17. The method claim 16, further comprising:

capacitively coupling the two electrically conducting proof masses to the AC ground.

18. The method of claim 15, further comprising

connecting the electrical-resistance mid-point to AC ground.

19. The method of claim 18, further comprising:

capacitively coupling the two electrically conducting proof masses to one or more sense capacitance electrodes having bias voltages; and

connecting an input of the sense charge amplifier to the one or more sense capacitance electrodes.

20. A tuning fork gyroscope that is insensitive to magnetic field gradients, the tuning fork gyroscope comprising:

means to suspend a first conductive proof mass and a second conductive proof mass over at least one insulating substrate;

means to couple the first conductive proof mass and the second conductive proof mass to AC ground; and

means to generate an output signal indicative of the tuning fork resonant mode, the means to generate being operable to receive an input from an electrical-resistance mid-point of the means to suspend, wherein the generated output signal is unaffected when the first conductive proof mass and the second conductive proof are subjected to a magnetic field gradient.

21. A magnetic gradiometer comprising:

a first electrically conducting proof mass connected through electrically conducting suspensions to anchors attached to one or more insulating substrates;

a second electrically conducting proof mass connected through electrically conducting suspensions to the anchors attached to the one or more insulating substrates, wherein the first electrically conducting proof mass and the second electrically conducting proof mass are capacitively coupled to DC ground and are driven to move in an oscillatory motion with opposing velocities along a motor axis; and

a sense charge amplifier configured to receive a first input from one of the anchors and to receive a second input from DC ground, wherein the sense charge amplifier generates an output signal indicative of a magnetic field gradient to which the first electrically conducting proof mass and the second electrically conducting proof mass are exposed.

22. A magnetic gradiometer comprising:

a first electrically conducting proof mass and a second electrically conducting proof mass driven to move in an oscillatory motion with opposing velocities along a motor axis;

a first end of the first electrically conducting proof mass connected through electrically conducting suspensions to a first anchor attached to an insulating substrate;

a first end of the second electrically conducting proof mass connected through electrically conducting suspensions to the first anchor;

a second end of the first electrically conducting proof mass connected through electrically conducting suspensions to a second anchor attached to the insulating substrate;

a second end of the second electrically conducting proof mass connected through electrically conducting suspensions to the second anchor; and

a readout amplifier configured to receive a first input from the first anchor and to receive a second input from the second anchor, wherein the sense charge amplifier generates an output signal indicative of a magnetic field gradient to which the first electrically conducting proof mass and the second electrically conducting proof mass are exposed.