MEMS GyroscopeMEMS GyroscopeAaron BurgAaron Burg

Azeem MeruaniAzeem MeruaniMichael WickmannMichael Wickmann

Robert SandheinrichRobert Sandheinrich

GyroscopesGyroscopes

Intro to GyroscopesIntro to GyroscopesDraper Tuning fork GyroscopeDraper Tuning fork GyroscopePiezoelectric GyroscopePiezoelectric GyroscopeAbsolute Angle Measurement using a Absolute Angle Measurement using a GyroscopeGyroscopeOptical Gyroscope and limitationsOptical Gyroscope and limitationsApplicationsApplications

Intro to GyroscopesIntro to Gyroscopes

Traditional GyroscopesTraditional GyroscopesWorking PrincipleWorking PrincipleTransition to MEMSTransition to MEMSTypes of GyroscopesTypes of Gyroscopes PiezoelectricPiezoelectric VibratoryVibratory Ring LaserRing Laser

Laser Ring GyroscopesLaser Ring Gyroscopes

Two signals sent around ringTwo signals sent around ringDifferent path lengths create a Different path lengths create a beat frequency.beat frequency.

AA – – area of ringarea of ring

P – P – perimeter of ringperimeter of ring

pA

4

Dead BandDead Band

Dead Band -No change Dead Band -No change in beat frequency for in beat frequency for small rotation ratessmall rotation ratesDue to frequency “lock-Due to frequency “lock-in”in”

r- backscattering r- backscattering amplitudeamplitude

Acr

L 2

Scaling DifficultiesScaling Difficulties

Derived Equation for Laser GyroscopeDerived Equation for Laser Gyroscope

Beat Freq = (M) Angular Velocity - 1/MBeat Freq = (M) Angular Velocity - 1/M Dead Band = 1/M^2 Dead Band = 1/M^2

M = Scaling FactorM = Scaling Factor

Scaling DifficultiesScaling Difficulties

M = 10M = 10-4-4

--Dead Band = 10Dead Band = 1088 times times biggerbigger-Time varying term larger-Time varying term larger-Slope of response lower-Slope of response lower

Change BandwidthChange Bandwidth

To lower Dead Band, wavelength To lower Dead Band, wavelength could be decreased.could be decreased.

Lower slope – Decreased Lower slope – Decreased SensitivitySensitivity

Acr

L 2

Draper Tuning Fork GyroDraper Tuning Fork Gyro

The rotation of tines The rotation of tines causes the Coriolis causes the Coriolis ForceForceForces detected Forces detected through either through either electrostatic, electrostatic, electromagnetic or electromagnetic or piezoelectric.piezoelectric.Displacements are Displacements are measured in the measured in the Comb driveComb drive

AdvancementsAdvancements

Improvement of driftImprovement of driftImprovement of Improvement of resolutionresolution

0

0.2

0.4

0.6

0.8

1

1.2

drift '93 drift '98

Deg

/ hr

0

500

1000

1500

2000

2500

3000

3500

4000

4500

Resolution '93 Resolution ' 94 Resolution '97

Deg

/ hr

Performance AdvantagesPerformance Advantages

No change in performance due to No change in performance due to temperature temperature Lower voltage noise Lower voltage noise Stronger signal to noise ratioStronger signal to noise ratio Better communication with external devicesBetter communication with external devices Higher sensitivityHigher sensitivity

Piezoelectric GyroscopesPiezoelectric Gyroscopes

Basic PrinciplesBasic Principles Piezoelectric plate with Piezoelectric plate with

vibrating thicknessvibrating thickness Coriolis effect causes Coriolis effect causes

a voltage form the a voltage form the materialmaterial

Very simple design Very simple design and geometryand geometry

Piezoelectric GyroscopePiezoelectric Gyroscope

AdvantagesAdvantages Lower input voltage than vibrating massLower input voltage than vibrating mass Measures rotation in two directions with a Measures rotation in two directions with a

single devicesingle device Adjusting orientation electronically is possibleAdjusting orientation electronically is possible

DisadvantagesDisadvantages Less sensitiveLess sensitive Output is large when Output is large when ΩΩ = 0 = 0

Absolute Angle MeasurementAbsolute Angle Measurement

Bias errors cause a drift while integratingBias errors cause a drift while integratingAngle is measured with respect to the Angle is measured with respect to the casingcasing The mass is rotated with an initial The mass is rotated with an initial θθ When the gyroscopes rotates the mass When the gyroscopes rotates the mass

continues to rotate in the same directioncontinues to rotate in the same direction

Angular rate is measured by adding a Angular rate is measured by adding a driving frequency driving frequency ωωdd

Design considerationDesign consideration

Damping needs to be Damping needs to be compensated compensated Irregularities in Irregularities in manufacturingmanufacturingAngular rate Angular rate measurementmeasurement

For angular rate measurement

Compensation force

APPLICATIONSAPPLICATIONS

Anti-Lock BrakesAnti-Lock BrakesMilitary MunitionsMilitary MunitionsInertial Measurement UnitInertial Measurement UnitGait-Phase Detection Sensor Embedded Gait-Phase Detection Sensor Embedded in a Shoe Insolein a Shoe Insole

Anti-Lock BrakesAnti-Lock Brakes

Use of Draper Tuning Fork GyroscopeUse of Draper Tuning Fork GyroscopeYaw Rate Sensor for skid controlYaw Rate Sensor for skid controlTested under rigorous temperature conditionsTested under rigorous temperature conditions

Inertial Measurement UnitInertial Measurement Unit

Honeywell acquired Honeywell acquired Draper’s Tuning Fork Draper’s Tuning Fork technologiestechnologiesReplaced Ring Laser Replaced Ring Laser Gyro in original Gyro in original designdesignDeveloped a low-cost, Developed a low-cost, micro-device capable micro-device capable of accurately of accurately measuring rates and measuring rates and displacementsdisplacements

Munitions ControlsMunitions ControlsDraper Laboratories working Draper Laboratories working with Office of Naval Research with Office of Naval Research to develop countermeasure-to develop countermeasure-proof munitionsproof munitionsTuning Fork Gyroscope used Tuning Fork Gyroscope used for positioning and rates of for positioning and rates of displacementdisplacementGyro allows for inertial Gyro allows for inertial movement, bypassing movement, bypassing countermeasurescountermeasures

Gait-Phase Detection sensor Gait-Phase Detection sensor Embedded in a Shoe Insole Embedded in a Shoe Insole

Measures the angular velocity of the footMeasures the angular velocity of the footUsed to activate a functional electrical stimulator Used to activate a functional electrical stimulator attached to the foot.attached to the foot.Over 96% accuracyOver 96% accuracy

ConclusionConclusion