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MicroElectroMechanical Systems (MEMS) Inertial Measurement Unit ( IMU). Attitude relative to gravity vector Magnetic heading Rotational velocity Translational acceleration. Positives. Absolute rotational attitude of object Direct measurement of angular velocity
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MicroElectroMechanical Systems (MEMS) Inertial Measurement Unit (IMU) • Attitude relative to gravity vector • Magnetic heading • Rotational velocity • Translational acceleration IMU
Positives • Absolute rotational attitude of object • Direct measurement of angular velocity • Direct measurement of translational acceleration IMU
Negatives • Does not provide – • absolute location • translational velocity • rotational acceleration • Data communication • Medium resolution • < 150 Hz IMU
History of IMUs • Vehicle navigation • Intercontinental ballistic missiles (ICBM) • Nuclear submarines • Cruise missiles • MEMS • Automotive • Consumer products IMU
MEMS IMUs - Automotive • Automotive • Accelerometers to deploy airbags • Vehicle roll handling IMU
MEMS IMUs – Consumer Products • Games (WiiMote) • PDA (iPhone) • Camera stabilization • Hard disks IMU
MEMS Fabrication IMU
MEMS accelerometer(proof mass) gravity acceleration IMU
MEMS IMU Outputs • Signal • Analog voltage (0 to 3V) • Fixed frequency, variable duty cycle • Digital (internal A/D converter) • Nominal Bandwidth • 550 Hz for accelerometer • 150 Hz for gyro • 50 Hz for magnetometer IMU
Two-Dimensional (2D) IMU • Biaxial accelerometer • Uniaxial gyro IMU
az ay ax Three-Dimensional (3D) IMU • Triaxial accelerometer • Triaxial gyro • Triaxial magnetometer • Required to determine spin about gravity vector IMU
9DOF Board – Sparkfun • Triaxial accelerometer • ±3g, 300 mV/g, 550 Hz • Triaxial gyro • ±300 deg/sec (dps), 3.3mV/dps, 140 Hz • Triaxial magnetometer • 50 Hz • On-board CPU, serial I/O IMU
9DOF Chip – Invensense MPU-9150 • Triaxial accelerometer • ±2g, ±4g, ±8g and ±16g • Triaxial gyro • ±250, ±500, ±1000, and ±2000dps • Triaxial compass • On-board motion fusion, I2C serial MEMS IMU