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EECS 373
Gyroscopes
Kevin Chyn
Scott Perry
Brian Schlenker
http://embeddedsystemnews.com/stmicroelectronics-introduces-a-new-family-
of-single-and-multi-axis-mems-micro-electro-mechanical-systems-
gyroscopes.html
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Outline
• Introduction to Gyroscopes
– Theory of operation
– Applications
• Historic and Modern Varieties
– History of gyroscopes
– Current technology
• Implementation
– Algorithms
– Feedback and control
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What is a Gyroscope?
•Device used to measure or maintain orientation
•Works on the principals of angular momentum
• Initial axis of rotation is conserved
•Consists of a spinning mass on an axel
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How Gyroscopes Work
•Mechanical Gyroscope
• Spinning mass mounted on gimbals
• Free-output vs. Fixed-output
• Sensors on axis to detect rotation
• Procession
•Electronic Gyroscope
• Coriolis vibratory gyroscope
• Proof mass fed oscillating current to induce
vibrations
• Vibrating mass tends to oscillate in initial plane of
reference
• When rotated, oscillations in orthogonal plane
detected by circuitry
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Common Uses
Gyrocompass
•Used by ships to find true north
•Seeks minimum potential energy
Stability Assistance
•Hubble Space Telescope
•Bicycles
Inertial Guidance System
• Guided Missiles
•Measure angular velocity in inertial reference frame
•Detect changes to orientation
•Combined with accelerometer for 6 axis sensor
7. History of Gyroscopes
• Initially a toy, not a tool
– Tops were common in ancient civilizations
– Began to be used in naval navigation and science
during the 18th
and 19th
centuries
1852 French gyroscope used
to measure Earth’s rotation
1860 gyro used to model orbital
motion
8. History of Gyroscopes
• Integration with electronics
– In the early 20th
century, gyroscopes became combine
with electric motors, allowing them to operate without
mechanical power
– Miniaturized during WWII for torpedo, ship, and plane
navigation
– Further miniaturized with the advent for silicon-based
electronics
WWII era bomb release control
mechanism Common $50 consumer
gyroscope available on Sparkfun
9. Types of Gyroscopes
• Rotary gyroscope
– Rotor suspended in a gambol spins independently in order
to conserve angular momentum
– Mostly unused in modern systems
• Fiber optic gyroscope (FOG)
– Fiber optic coil determines changes in orientation by path
of light in the coil
– Beam traveling against rotation has slightly shorter path
• Microelectromechanical systems (MEMS)
– Uses very small vibrating mechanism to detect changes
• London moment
– Spinning superconductor generates a magnetic field
– Extremely accurate tool or modern science
10. Common Gyroscope Criteria
• Performance
– Measurement range
– Number of sensing axes
– Nonlinearity
– Bandwidth
– Angular Random Walk (ARW)
– Bias
– Bias Drift
– Bias Instability
• Specifications
– Cost
– Working temperature range
– Shock survivability
– Size/Mass
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General Algorithms
•Noise reduction via low pass filter
•Scale calibration to get meaning from gyroscope data
•Integrate data over time to get “absolute angle”
•Enhancement using Kalman filter
• Can reduce/eliminate integration drift
14. Inertial Navigation Systems
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• Dead reckoning – using previous position to determine
current position
• Used on ships, aircraft, submarines, missiles,
spacecraft, etc
• Firefighters/military – step based INS
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GPS
• Low refresh rate
– 10Hz? 20Hz?
• Relatively low resolution
– Location to n meters
• Limited to outdoors
INS
• High refresh rate
– Kilohertz
• Relatively high resolution
– But prone to drift
• Doesn’t rely on satellites
Combine both sensors using Kalman Filter to
produce highly accurate results
GPS/INS
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17. Feedback Control Systems
Optical Image Stabilization
• Vibration detected using
gyroscopes
• Movements modeled as
sinusoid
• Lens is shifted to
counteract vibration
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