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Inertial Sensors

Inertial Sensors. Inertial Sensors? Inertial sensors in inertial navigation : big & expensive MEMS(Micro-Electro-Mechanical Systems) Technology Accelerometer Types pendulous accelerometer vibrating beam accelerometers Gyroscopes Types mechanical gyroscope Dynamically Tuned gyroscope

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Inertial Sensors

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  1. Inertial Sensors • Inertial Sensors? • Inertial sensors in inertial navigation : big & expensive • MEMS(Micro-Electro-Mechanical Systems) Technology • Accelerometer Types • pendulous accelerometer • vibrating beam accelerometers • Gyroscopes Types • mechanical gyroscope • Dynamically Tuned gyroscope • vibrating gyroscope • optical gyroscope (Fiber-optic gyro, ring laser gyro)

  2. Inertial Navigation • Inertial Navigation • A typical inertial navigation system integrates the information gather from a combination of gyroscopes and accelerometers in order to determine the current state of the system. • Western Inertial Markets • ICBM Trident D5 accuracy : CEP 111 m at 7400 Km (about Korea – Hawaii)

  3. Accelerometer Principle • mass-spring type accelerometer • To increase accelerometer sensitivity : m large or K small

  4. ADXL 202 Dual Axis Accelerometers • Analog Device ADXL202 • surface-micromachined accelerometer • Sensor Principle • To increase accelerometer sensitivity : • large m, small K, large A measure capacitance, which is inversely proportional to the gap

  5. ADXL 202 Dual Axis Accelerometers • To increase the mass, common beam mass is used x direction acceleration is detected here y x spring

  6. ADXL202 Spec • ADXL202 Diagram & Features

  7. ADXL203 Spec

  8. Accelerometer resolution • 10 bit A/D converter : 1024 division • A/D converter : 1024 div : 5v  4.88 mv/div  about 5mv/div • 1 mg/mv • resolution : 5mg • 12 bit A/D converter : 4096 division • A/D converter : 4096 div : 5V  1.22mv/div • resolution : 1.22 mg / div • accelerometer noise level • 0.11*0.11 mg^2 / Hz * 60 Hz = 0.726 mg^2  square root  0.85 mg? • 12 bit A/D converter in practice • A/D converter noise 2.5 mg (2div) + accelerometer noise 0.85 mg • about 4-5 mg? • Bias & scale factor!

  9. Gyroscope • Gyroscopic Precession • What will happen if there is rotation around the rotation axis

  10. Precession of a gyroscope

  11. Gyroscope based on gyroscopic precession • Single-axis Gyroscope

  12. Coriolis Acceleration • Coriolis acceleration • A person moving northward toward the outer edge of a rotating platform must increase the westward speed component (blue arrows) to maintain a northbound course. The acceleration required is the Coriolis acceleration.

  13. Coriolis Acceleration • Constrained motion means force is applied turning fork gyroscope ADXRS150

  14. Gyroscope using Coriolis effect • Schematic of the gyro’s mechanical structure • The displacement is proportional to the rotation speed

  15. ADXRS 150 Single Axis Gyroscope • ADXRS150 gyroscope structure opposite drive direction (robust to shock & vibration)

  16. ADXRS spec • ADXRS150 Diagram & Features

  17. ADXRS150 Spec.

  18. Gyroscope resolution • 10 bit A/D converter • about 5mv/div • 0.08 deg/sec / mv • resolution : 0.4 deg/sec • 12 bit A/D converter • resolution : 0.1 deg/sec • gyroscope noise level • 0.05*0.05 deg/sec / Hz * 60 Hz = 0.15 (deg/sec)^2  square root  0.38 deg/sec • gyroscope resolution • 0.5 deg/sec ???

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