1 Inertial Sensors Inertial Sensors? Inertial sensors in inertial navigation : big & expensive MEMS(Micro-Electro-Mechanical Systems) Technology Accelerometer.

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Inertial SensorsInertial 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)

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Inertial NavigationInertial 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)

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Accelerometer PrincipleAccelerometer Principle

mass-spring type accelerometer

• To increase accelerometer sensitivity : m large or K small

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ADXL 202 Dual Axis AccelerometersADXL 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

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ADXL 202 Dual Axis AccelerometersADXL 202 Dual Axis Accelerometers

To increase the mass, common beam mass is used

x

y

x direction acceleration is detected here

spring

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ADXL202 SpecADXL202 Spec

ADXL202 Diagram & Features

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ADXL203 SpecADXL203 Spec

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Accelerometer resolutionAccelerometer 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!

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Gyroscope Gyroscope

Gyroscopic Precession

• What will happen if there is rotation around the rotation axis

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Precession of a gyroscopePrecession of a gyroscope

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Gyroscope based on gyroscopic precessionGyroscope based on gyroscopic precession

Single-axis Gyroscope

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Coriolis AccelerationCoriolis 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.

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Coriolis Acceleration Coriolis Acceleration

Constrained motion means force is appliedturning fork gyroscope

ADXRS150

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Gyroscope using Coriolis effectGyroscope using Coriolis effect

Schematic of the gyro’s mechanical structure

The displacement is proportional to the rotation speed

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ADXRS 150 Single Axis GyroscopeADXRS 150 Single Axis Gyroscope

ADXRS150 gyroscope structure

opposite drive direction

(robust to shock & vibration)

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ADXRS specADXRS spec

ADXRS150 Diagram & Features

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ADXRS150 Spec.ADXRS150 Spec.

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Gyroscope resolutionGyroscope 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 ???