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Bias measurement for MEMS gyroscopes and accelerometers

  • US 8,397,568 B2
  • Filed: 04/24/2007
  • Issued: 03/19/2013
  • Est. Priority Date: 04/24/2006
  • Status: Expired due to Fees
First Claim
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1. A MEMS integrated inertial measurement unit (IMU) for a vehicle that has body X and Y axes, comprising:

  • a) a substrate;

    b) at least two, coplanar, inertial measurement instruments, both coupled to the substrate, the inertial measurement instruments comprising a generally planar single degree of freedom (DOF) MEMS gyroscope and a generally planar single DOF MEMS accelerometer, each inertial measurement instrument comprising a planar sensing member, wherein each inertial measurement instrument exhibits a bias instability that has a frequency, and wherein each inertial measurement instrument defines an input axis that is in the plane of the sensing member and is aligned with either the body X axis or the body Y axis;

    c) wherein the gyroscope is adapted to sense rotations of the substrate about the gyroscope input axis and is essentially insensitive to rotations about two axes that are each orthogonal to the gyroscope input axis, to accomplish a single DOF gyroscope, the gyroscope having a gyroscope output signal that is related to the rate of rotation about the gyroscope input axis;

    d) wherein the accelerometer is adapted to sense accelerations of the substrate along the accelerometer input axis and is essentially insensitive to accelerations about two axes that are each orthogonal to the accelerometer input axis, to accomplish a single DOF accelerometer, the accelerometer having an accelerometer output signal that is related to the rate of acceleration along the accelerometer input axis;

    e) a planar platform that carries the substrate and that defines a platform plane that is essentially parallel to the planes of the planar sensing members, such that the input axes of the gyroscope and the accelerometer are essentially parallel to the platform plane;

    f) a system that rotates the platform through 360 degrees at a constant rotation rate about a platform rotation axis that is orthogonal to the platform plane, the rotation at a frequency that is greater than the bias instability frequency;

    g) a pick-off that is used to measure the rotation angle of the platform and generate a reference waveform; and

    h) a phase-sensitive detection system that;

    i) mixes the reference waveform with the gyroscope output signal to obtain the rotation rate about the gyroscope input axis;

    ii) mixes the reference waveform with the accelerometer output signal to obtain the acceleration rate about the accelerometer input axis;

    iii) phase shifts the reference waveform by 90 degrees;

    iv) mixes the phase-shifted waveform with the gyroscope output signal to obtain the rotation rate about an axis in the plane of the sensing member and orthogonal to the gyroscope input axis; and

    v) mixes the phase-shifted waveform with the accelerometer output signal to obtain the acceleration rate about an axis in the plane of the sensing member and orthogonal to the accelerometer input axis.

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