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 y x direction acceleration is detected here 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 = 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 ???