EECS 373

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EECS 373 Gyroscopes Kevin Chyn Scott
Perry Brian Schlenker
http//embeddedsystemnews.com/stmicroelectronics-i
ntroduces-a-new-family-of-single-and-multi-axis-me
ms-micro-electro-mechanical-systems-gyroscopes.htm
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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

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• Consumer Electronics
• Wii Remote
• Tilt, yaw, pitch
• Rate of angular movement
• Smart Phones
• Screen Orientation
• Gaming Input
• Laptops
• Free fall detection

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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 Earths
rotation
1860 gyro used to model orbital motion
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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
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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

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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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Angular Random Walk

•  

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Examination of Recent Gyros
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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

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Inertial Navigation Systems

• 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/INS
GPS
INS

• Low refresh rate
• 10Hz? 20Hz?
• Relatively low resolution
• Location to n meters
• Limited to outdoors

• High refresh rate
• Kilohertz
• Relatively high resolution
• But prone to drift
• Doesnt rely on satellites

Combine both sensors using Kalman Filter to
produce highly accurate results
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Feedback Control Systems

• Optical Image Stabilization

• Vibration detected using gyroscopes
• Movements modeled as sinusoid
• Lens is shifted to counteract vibration

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Refrences

• http//physics.kenyon.edu/EarlyApparatus/Mechanics
  /Gyroscope/Gyroscope.html
• http//solarsystem.nasa.gov/scitech/display.cfm?ST
  _ID327
• http//orgs.usd.edu/nmm/News/Newsletter/August2010
  /ConnResearch.html
• http//www.sensorwiki.org/doku.php/sensors/gyrosco
  pe