global positioning system integrated with an inertial navigation system michael bekkala michael...
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Global Positioning System Integrated with an Inertial Navigation System
Michael BekkalaMichael Blair
Michael CarpenterMatthew Guibord
Abhinav ParvataneniDr. Shanker Balasubramaniam
Inertial Navigation System
The use of inertial measurements in navigation
Measurements come from inertial sensors such as:• Accelerometers• Gyroscopes
Very accurate over short term Errors integrate with time
Physics of Accelerometers/Gyroscopes
Accelerometers• Measure acceleration in x, y, z
directions• Types:
MechanicalMicro Electromechanical (MEMS)
• Capacitive• Piezoelectric
Mechanical Accelerometers
Mass suspended in a case by a pair of springs
Acceleration along the axis of the springs displaces the mass.
This displacement is proportional to the applied acceleration
Picture from “Basic Inertial Navigation” by Sherryl Stoval
Capacitive Accelerometers
Sense a change in capacitance with respect to acceleration
Diaphragm acts as a mass that undergoes flexure
Two fixed plates sandwich diaphragm, creating two capacitors
Change in capacitance by altering distance between
two plates
http://www.sensorland.com/HowPage011.html
Piezoelectric Accelerometers
Commonly uses 1 crystalmade of quartz
Force exerted by acceleration changes electrostatic force Low output signal and high
output impedance requiresthe use of amplifiers
Picture from Wikipedia.org
Physics of Accelerometers/Gyroscopes
Gyroscopes• Measure Angular velocity in yaw,
pitch, and roll directionsMicro Electromechanical (MEMS)Optical
Micro Electromechanical Gyroscopes
• Coriolis effect• Vibrating elements measure
Coriolis effect (vibrations on sense axis)
• When rotated, 2nd vibration on the drive axis• Angular Velocity
Picture from http://www.howyourelectronicswork.com/2008/09/fiber-optic-gyroscopes.html
Optical Gyroscopes
Sends out two beams of light Sensor can detect interference in the light
beam Very accurate No inherent drift Expensive
Navigation Equations
Accelerations and angular velocities are measured in the body coordinate frame
Need a constant reference for navigation
Rotation from bodyframe to North, East,Down frame gives areference.
Picture from “Accuracy and Improvement of Low Cost INS/GPS for Land Applications” by Shin
Inertial Navigation System
Diagram from Basic Inertial Navigation by Sherryl Stovall
System View of INS Equations
Navigation Equations
The navigation equations can be represented as (Shin, 2001):
100
0cos)(
10
00)(
1
)(
)2(
1
1
hR
hR
D
C
gvfC
vD
C
v
r
e
e
bin
bib
nb
nnnen
nie
bnb
n
nb
n
n
Navigation Equations
BodyNED
Roll
Pitchθ
Yawψ
cossin0
sincos0
001
cosθ0sinθ
010
sinθ0cosθ
100
0cosψsinψ
0sinψcosψ
CNB
Navigation Equations
GPS and INS need to be in the same reference frame for proper measurements.
GPS data is in Earth Centered Earth Fixed (ECEF)
INS data is in Body frameand has to be translated to the North-East-Down frame
BodyNED, ECEFNEDPicture from “Accuracy and Improvement of Low Cost INS/GPS for Land Applications” by Shin
Integration of GPS and INS
Different integration levels:• Loosely Coupled
Corrects errors in the IMU and INS Does not correct GPS
• Tightly Coupled Corrects both INS and GPS errors
Kalman filtering integrates both systems to achieve a more accurate overall system
GPS/INS Integration
Diagram from http://inderscience.metapress.com/media/59dam5dyxldjpg54uc5v/contributions/8/3/w/2/83w217t06m878447.pdf
System View of Integration