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Small angle bias measurement mechanism for MEMS instruments

  • US 7,549,334 B2
  • Filed: 04/24/2007
  • Issued: 06/23/2009
  • Est. Priority Date: 04/24/2006
  • Status: Expired due to Fees
First Claim
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1. A method for separating bias instability of a rotating MEMS gyroscope having an output signals from the gyroscope'"'"'s output signal, in which the bias instability has a frequency, the method comprising:

  • (a) providing a bias-stabilized gyroscope that lies generally in a plane, for detecting rotation rate about a gyro input axis that lies in the plane, the gyroscope comprising;

    a substrate defining a surface;

    spaced bonding pads coupled to the substrate and projecting from the surface of the substrate;

    a generally planar gimbal spaced from and essentially parallel to the surface of the substrate and flexibly coupled to the bonding cads by gimbal flexures, such that the gimbal is capable of rotary oscillatory motion relative to the substrate about a Z axis that is orthogonal to the plane of the gimbal;

    a generally planar plate gyro outer member located within, coplanar with, and flexibly coupled to the gimbal such that the gyro outer member is capable of oscillatory motion relative to the substrate about a drive axis that is in the plane of the gyro outer member and orthogonal to the input axis;

    a generally planar plate gyro inner member located within, coplanar with, and flexibly coupled to the gyro outer member such that the gyro inner member is capable of rotary oscillatory motion relative to the gyro outer member about an output axis that is orthogonal to the plane of the gyro inner and outer members in response to input rotation rate, and such that the gyro inner member will oscillate with the gyro outer member relative to the substrate about the drive axis, as the gyro outer member is oscillated about the drive axis;

    one or more gimbal drives for oscillating the gimbal about the Z axis at a gimbal oscillation frequency, and thereby also oscillating the gyro inner and outer members about the Z axis at the gimbal oscillation frequency;

    one or more gyro outer member drives for directly oscillating the gyro outer member about the drive axis, and thereby also oscillating the gyro inner member about the drive axis;

    one or more gyro outer member motion sensors that sense motion of the gyro outer member relative to the substrate about the drive axis; and

    one or more gyro inner member motion sensors having an output signal, the gyro inner member motion sensors detecting oscillation of the gyro inner member relative to the gyro outer member about the output axis caused by rotation of the gyroscope about the gyro input axis;

    (b) providing the gimbal drives with an oscillatory excitation signal that oscillates the gimbal at a frequency that is greater than the bias instability frequency;

    (c) detecting the gyro inner member motion sensors output signal; and

    (d) demodulating the gyro inner member motion sensors output signal with the gimbal drive oscillatory excitation signal, phase referenced to the gyro input axis.

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