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

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Consumer Electronics

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Wii Remote Tilt, yaw, pitch Rate of angular movement

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Smart Phones Screen Orientation Gaming Input

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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 18 th and 19 th centuries 1852 French gyroscope used to measure Earth ’ s rotation 1860 gyro used to model orbital motion

History of Gyroscopes

• Integration with electronics – In the early 20 th 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

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

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 11

Examination of Recent Gyros 12

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 • 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 15

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_ID

=327 • http://orgs.usd.edu/nmm/News/Newsletter/August20 10/ConnResearch.html

• http://www.sensorwiki.org/doku.php/sensors/gyrosco pe