US20030033850A1 - Cloverleaf microgyroscope with electrostatic alignment and tuning - Google Patents

Cloverleaf microgyroscope with electrostatic alignment and tuning Download PDF

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Publication number
US20030033850A1
US20030033850A1 US09/927,858 US92785801A US2003033850A1 US 20030033850 A1 US20030033850 A1 US 20030033850A1 US 92785801 A US92785801 A US 92785801A US 2003033850 A1 US2003033850 A1 US 2003033850A1
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United States
Prior art keywords
gyroscope
micro
axis
detecting
drive
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Abandoned
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US09/927,858
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English (en)
Inventor
A. Challoner
Roman Gutierrez
Tony Tang
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Boeing Co
California Institute of Technology CalTech
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Boeing Co
National Aeronautics and Space Administration NASA
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Priority to US09/927,858 priority Critical patent/US20030033850A1/en
Application filed by Boeing Co, National Aeronautics and Space Administration NASA filed Critical Boeing Co
Assigned to CALIFORNIA INSTITUTE OF TCHNOLOGY reassignment CALIFORNIA INSTITUTE OF TCHNOLOGY ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: GUTIERREZ, ROMAN C., TANG, TONY K.
Assigned to BOEING COMPANY, THE reassignment BOEING COMPANY, THE ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: CHALLONER, A. DORIAN
Assigned to KATHY BAYER reassignment KATHY BAYER CONFIRMATORY LICENSE (SEE DOCUMENT FOR DETAILS). Assignors: CALIFORNIA INSTITUTE OF TECHNOLOGY
Priority to AU2002355525A priority patent/AU2002355525A1/en
Priority to PCT/US2002/023224 priority patent/WO2003014669A2/fr
Priority to JP2003519353A priority patent/JP2005530124A/ja
Priority to EP02752502.1A priority patent/EP1421331B1/fr
Assigned to NATIONAL AERONAUTICS AND SPACE ADMINISTRATION reassignment NATIONAL AERONAUTICS AND SPACE ADMINISTRATION CORRECTIVE ASSIGNMENT TO CORRECT THE NAME OF THE ASSIGNEE PREVIOUSLY RECORDED ON REEL 012685 FRAME 0485 Assignors: CALIFORNIA INSTITUTE OF TECHNOLOGY
Publication of US20030033850A1 publication Critical patent/US20030033850A1/en
Priority to US10/843,139 priority patent/US7159441B2/en
Abandoned legal-status Critical Current

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
    • G01C19/00—Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
    • G01C19/56—Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces
    • G01C19/5719—Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces using planar vibrating masses driven in a translation vibration along an axis
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
    • G01C19/00—Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
    • G01C19/56—Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
    • G01C25/00—Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
    • G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
    • G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
    • G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
    • G01P2015/0805—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration
    • G01P2015/0822—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration for defining out-of-plane movement of the mass
    • G01P2015/084—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration for defining out-of-plane movement of the mass the mass being suspended at more than one of its sides, e.g. membrane-type suspension, so as to permit multi-axis movement of the mass
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
    • G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
    • G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
    • G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
    • G01P2015/0805—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration
    • G01P2015/0822—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration for defining out-of-plane movement of the mass
    • G01P2015/084—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration for defining out-of-plane movement of the mass the mass being suspended at more than one of its sides, e.g. membrane-type suspension, so as to permit multi-axis movement of the mass
    • G01P2015/0842—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration for defining out-of-plane movement of the mass the mass being suspended at more than one of its sides, e.g. membrane-type suspension, so as to permit multi-axis movement of the mass the mass being of clover leaf shape

Definitions

  • the present invention relates to micro-machined electromechanical systems, and more particularly to a MEMS vibratory gyroscope having closed loop output.
  • Micro-gyroscopes are used in many applications including, but not limited to, communications, control and navigation systems for both space and land applications. These highly specialized applications need high performance and cost effective micro-gyroscopes.
  • the prior art gyroscope has a resonator having a “cloverleaf” structure consisting of a rim, four silicon leaves, and four soft supports, or cantilevers, made from a single crystal silicon.
  • a metal post is rigidly attached to the center of the resonator, in a plane perpendicular to the plane of the silicon leaves, and to a quartz base plate with a pattern of electrodes that coincides with the cloverleaf pattern of the silicon leaves.
  • the electrodes include two drive electrodes and two sense electrodes.
  • the micro-gyroscope is electrostatically actuated and the sense electrodes capacitively detect Coriolis induced motions of the silicon leaves.
  • the response of the gyroscope is inversely proportional to the resonant frequency and a low resonant frequency increases the responsivity of the device.
  • Micro-gyroscopes are subject to electrical interference that degrades performance with regard to drift and scale factor stability. Micro-gyroscopes often operate the drive and sense signals at the same frequency to allow for simple electronic circuits. However, the use of a common frequency for both functions allows the relatively powerful drive signal to inadvertently electrically couple to the relatively weak sense signal.
  • the present invention is a method for electrostatic alignment and tuning of a cloverleaf micro-gyroscope having closed loop operation.
  • a differential sense signal (S 1 -S 2 ) is compensated by a linear electronic filter and directly fed back by differentially changing the voltages on two drive electrodes (D 1 -D 2 ) to rebalance Coriolis torque, suppress quadrature motion and increase the damping of the sense axis resonance.
  • the resulting feedback signal is demodulated in phase with the drive axis signal (S 1 +S 2 ) to produce a measure of the Coriolis force and, hence, the inertial rate input.
  • the micro-gyroscope and method of alignment and tuning of the present invention detects residual mechanical imbalance of the cloverleaf micro-gyroscope by quadrature signal amplitude and corrects the alignment to zero by means of an electrostatic bias adjustment rather than mechanical balancing.
  • In-phase bias is also nulled by electronically coupling a component of drive axis torque into the output axis. Residual mistuning is detected by way of quadrature signal noise level, or a transfer function test signal and is corrected by means of an electrostatic bias adjustment.
  • the quadrature amplitude is used as an indication of misalignment and quadrature noise level, or a test signal level, is used as a tuning indicator for electrostatic adjustment of tuning.
  • FIG. 1 is an exploded view of a prior art vibratory micro-gyroscope having four electrodes
  • FIG. 2 is a block diagram of a prior art closed-loop micro-gyroscope
  • FIG. 3 is an example of a prior art circuit schematic for closed loop sense/open loop drive operation
  • FIG. 4 is an exemplary electrode arrangement for the method of electrostatic alignment and tuning according to the present invention, the electrode arrangement includes eight electrodes;
  • FIG. 5 is a flowchart of the method for electrostatic alignment and tuning according to the present invention.
  • the method of the present invention is applicable to a closed loop micro-gyroscope.
  • the closed loop micro-gyroscope is described in conjunction with FIGS. 1 through 3.
  • the closed loop control of the preferred embodiment will be described in accordance with a cloverleaf micro-gyroscope having four electrodes.
  • FIG. 1 is an exploded view of the micro-gyroscope 10 .
  • the cloverleaf micro-gyroscope 10 has a post 12 attached to a resonator plate 14 having a cloverleaf shape with petals labeled 1 , 2 , 3 , and 4 .
  • the cloverleaf resonator plate 14 is elastically suspended from an outer frame 16 .
  • a set of four electrodes 18 located under the resonator plate 14 , actuate the resonator plate and sense capacitance on the resonator plate 14 .
  • Drive electrodes D 1 and D 2 actuate movement of the resonator plate 14 and sense electrodes S 1 and S 2 sense capacitance.
  • a set of axes are labeled x, y and z to describe the operation of the micro-gyroscope.
  • Rocking the post 12 about the x-axis actuates the micro-gyroscope 10 .
  • the rocking motion is accomplished by applying electrostatic forces to petals 1 and 4 by way of a voltage applied to the drive electrodes, D 1 and D 2 .
  • ⁇ For a steady inertial rate, ⁇ , along the z-axis or input axis, there will be a displacement about the y-axis, or output axis, that can be sensed by the differential output of the sensing electrodes, S 1 -S 2 or V thy .
  • the displacement about the y-axis is due to the influence of a rotation induced Coriolis force that needs to be restrained by a counteracting force.
  • the closed-loop control circuit nulls displacement about the y-axis through linearized electrostatic torques.
  • the electrostatic torques are proportional to control voltages.
  • the two drive electrodes D 1 and D 2 produce linearized electrostatic torques about the x and y axes that are proportional to control voltages V tx and V ty .
  • D 1 and D 2 are defined as:
  • V o is a bias voltage
  • the linearized torques are defined as:
  • r o offset from x or y axis to control, or drive, electrode center
  • C o the capacitance of one control electrode
  • V o the bias voltage
  • d o electrode gap which is the nominal separation between the electrode plane and the resonator plane.
  • the control voltage V tx provides for automatic gain control of the drive amplitude.
  • the control voltage V ty provides for Coriolis torque re-balance.
  • the output axis (y-axis) gain and phase compensation are selected based on computed or measured transfer functions, G(s), from V ty to V thy .
  • the reference signal used to demodulate V ty is V thx which is in phase with the drive axis rate signal, ⁇ x .
  • the closed loop operation of the micro-gyroscope of the present invention measures the inertial rate, ⁇ , around the z-axis.
  • Signals S 1 and S 2 are output from pre-amplifiers 20 that are attached to the sense electrodes S 1 and S 2 .
  • the micro-gyroscope is set in motion by a drive loop 22 that causes the post to oscillate around the x-axis.
  • the post rocks and has a rate of rotation about the x-axis.
  • D 1 and D 2 apply voltages in phase therefore, they push and pull the resonator plate (not shown in FIG. 2) creating a torque, T x , on the x-axis.
  • S 1 and S 2 are in phase and indicate a rotation around the x-axis.
  • V thx S 1 +S 2 is amplitude and gain phase compensated in an automatic gain control loop 22 , 25 , 27 to 25 drive V thx to V tx .
  • An amplitude reference level, V r is compared with a comparator 23 to the output of the amplitude detector 22 that determines the amplitude of V thx .
  • the resulting amplitude error is gain and phase compensated 25 and applied as a gain to an automatic gain control multiplier 27 .
  • a drive voltage V tx proportional to V thx is thus determined that regulates the amplitude of the vibration drive.
  • V thy When an inertial rate is applied, it creates a difference between S 1 and S 2 equal to V thy .
  • V thy was merely sensed open loop as being proportional to the rate of the micro-gyroscope.
  • V thy is gain and phase compensated based on a computed, or measured, transfer function G(s).
  • G(s) the transfer function
  • the resulting closed loop output voltage V ty generates an electrostatic torque T y to balance the Coriolis torque, thereby nulling the motion on the output axis.
  • the rebalance torque voltage V ty is demodulated with the drive reference signal V thx by an output axis demodulator 29 and then processed through a demodulator and filter circuit 26 .
  • the DC component of the output signal of the demodulator, V out is proportional to the rotation rate ⁇ .
  • V thx and V thy are defined by:
  • V thx S 1+S2
  • V thy S 1 ⁇ S 2
  • R is the transimpedance from the preamplifiers 20 .
  • FIG. 3 is an example of a schematic for closed loop sense/open loop drive operation.
  • the present invention is applicable to either open loop or closed loop drive operation.
  • the two sense signals S 1 and S 2 are differenced, filtered and amplified.
  • the filter helps to remove residual second harmonics and adjusts loop phase to provide stable closed loop operation.
  • the following amplifiers serve to combine the closed loop output feedback signal with the open loop drive signal providing the correct signals to electrodes D 1 and D 2 . Rebalance of the Coriolis force and robust damping of the output axis resonance is provided by this wideband closed loop design.
  • the method of the present invention is best described herein with reference to an eight-electrode micro-gyroscope 100 shown in FIG. 4.
  • the closed loop control is very similar to that described in conjunction with FIGS. 1 - 3 .
  • D 1 and D 2 are used differentially for closed loop control on the y-axis and in common mode for x-axis control.
  • S 1 and S 2 are dedicated to differential y-axis output sensing.
  • S 3 senses the motion of the drive, or x-axis, and T 1 is used for tuning on x-axis.
  • Q 1 and Q 2 are used to align the micro-gyroscope.
  • the micro-gyroscope have closely tuned operation. Closely tuned operation has a drive frequency that is selected close to the sense axis natural resonant frequency for maximum mechanical gain. Symmetrical design and accurate construction of the micro-gyroscope are important so that the two rocking mode natural frequencies are similar. A self-resonant drive about the x-axis, for example an AGC loop, will permit large drive motion with small torque controls.
  • Misalignment is detected 102 by the presence of a quadrature signal amplitude on V out .
  • the misalignment is corrected 104 by an electrostatic bias adjustment to electrode Q 1 or Q 2 .
  • Residual mistuning is detected 108 and corrected 110 by way of an electrostatic bias adjustment to electrode T 1 .
  • the detection 108 is accomplished by noting the presence of a quadrature signal noise level or a transfer function test signal.
  • ⁇ o is the operating frequency of the drive and I xo is the drive amplitude.
  • ⁇ y - H ⁇ ( s ) - G ⁇ ( s ) ⁇ ⁇ R + L ⁇ ( s ) ⁇ ⁇ T + T c ⁇ ( s ) F ⁇ ( s ) + G ⁇ ( s ) ⁇ ⁇ x
  • ⁇ c ( J yy ⁇ o 2 ⁇ K yy )/( K( 1+ ⁇ c ) ⁇ o )
  • I o ( J yy 2 k ⁇ +D yx ⁇ R D yy ⁇ T D xx )
  • ⁇ bi ( D yx ⁇ R D yy ⁇ T D xx + ⁇ c ( ⁇ ( J yx ⁇ R J yy ) ⁇ o 2 +( K yx ⁇ R K yy ))/ ⁇ o )/2 kJ yy
  • ⁇ bq ( ⁇ c ( D yx ⁇ R D yy ⁇ T D xx )+( ⁇ ( J yx ⁇ R J yy ) ⁇ o 2 +( K yx ⁇ R K yy ))/ ⁇ o )/2 kJ yy
  • the remaining in-phase bias component of ⁇ bi can also be nulled. This can be accomplished by introducing a relative gain mismatch ⁇ T ⁇ 0 on the automatic gain control voltage to each of the drive electrodes D 1 and D 2 .
  • the cross-coupled electrostatic stiffness can be introduced by applying more or less bias voltage to one of the drive electrodes, D 1 or D 2 .
  • the in-phase rate bias error is also nulled as described above.
  • electrostatic cross-coupled stiffness, K e xy for alignment purposes can be introduced by modification of the bias voltage of either Q 1 or Q 2 .
  • Electrostatic modification of net K xx for tuning purposes can be accomplished by increasing or decreasing the bias voltage T 1 as well.
  • the bias voltage applied to T 1 is made larger than the voltage applied to S 1 and S 2 .
  • the total stiffness is the elastic stiffness plus the electrostatic stiffness.
  • the total stiffness about the x-axis is lowered so that ⁇ nx is also lowered and brought into tune with ⁇ ny .
  • the present invention provides a tuning method for vibratory micro-gyroscopes in which one of the bias voltages is increased or decreased until a minimum value of the rms noise is obtained or until a transfer function indicates tuning.
  • a test signal may be maximized.
  • a bias on Q 1 or Q 2 will introduce cross axis electrostatic stiffness.
  • Q 1 bias is adjusted until the quadrature amplitude is nulled.
  • ⁇ T is adjusted until the rate output is nulled.
  • the electrostatic tuning bias, electrode T 1 is adjusted until closed loop quadrature or in-phase noise, or another tuning signal, is minimized.
US09/927,858 2001-08-09 2001-08-09 Cloverleaf microgyroscope with electrostatic alignment and tuning Abandoned US20030033850A1 (en)

Priority Applications (6)

Application Number Priority Date Filing Date Title
US09/927,858 US20030033850A1 (en) 2001-08-09 2001-08-09 Cloverleaf microgyroscope with electrostatic alignment and tuning
EP02752502.1A EP1421331B1 (fr) 2001-08-09 2002-07-19 Microgyroscope en feuille de trefle a alignement et syntonisation electrostatique
AU2002355525A AU2002355525A1 (en) 2001-08-09 2002-07-19 Method for electrostatically aligning and tuning a microgyroscope
JP2003519353A JP2005530124A (ja) 2001-08-09 2002-07-19 静電的整列および同調を有するクローバーリーフマイクロジャイロスコープ
PCT/US2002/023224 WO2003014669A2 (fr) 2001-08-09 2002-07-19 Microgyroscope en feuille de trefle a alignement et syntonisation electrostatique
US10/843,139 US7159441B2 (en) 2001-08-09 2004-05-11 Cloverleaf microgyroscope with electrostatic alignment and tuning

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US09/927,858 US20030033850A1 (en) 2001-08-09 2001-08-09 Cloverleaf microgyroscope with electrostatic alignment and tuning

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US10/843,139 Expired - Lifetime US7159441B2 (en) 2001-08-09 2004-05-11 Cloverleaf microgyroscope with electrostatic alignment and tuning

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EP (1) EP1421331B1 (fr)
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AU (1) AU2002355525A1 (fr)
WO (1) WO2003014669A2 (fr)

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WO2003014669A3 (fr) 2004-03-25
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