Transcript IMU / GPS Positioning System

IMU / GPS Positioning System
Center for Intelligent Machines and Robotics
Rommel E. Mandapat
Project Goals
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Develop a low cost positioning system by
integrating a Honeywell Inertial Measurement
Unit with Novatel Differential GPS
 Implement the IMU/GPS system on the
Navigation Test Vehicle using MAX
architecture
 The system performance of the IMU/GPS will
be evaluated against that of the existing
MAPS/GPS
Motivation & Approach
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For navigation of autonomous ground vehicle,
must have reliable real-time positioning system
capable of outputting data at over 10 Hz
Inertial Navigation Systems (INS) provide high
data rates but drift over time
DGPS provides high-accuracy position data but
at lower data rates (1-5 Hz). Also, GPS is
susceptible to data loss.
Integration of INS & GPS through an external
Kalman Filter will result in high-accuracy
position, velocity and attitude data at high rates
System Features
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Honeywell HG1700AG11 IMU
Novatel RT-20 differential GPS (DGPS)
PC-104 / Single Board computer platform
Primary and Secondary Kalman Filter (KF)
MAX message set
Data w/ 20 cm positional accuracy at 10 Hz
Honeywell HG1700AG11 IMU
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Strapdown inertial system
Three Ring Laser Gyros (RLG) measure angular
changes about roll, pitch and yaw axes
Three single-axis Accelerometers measure
velocity changes in the vehicle x, y, and z
directions
Inertial message output at 100 Hz (, , ,
Vx, Vy, Vz)
1 MHz output clock rate
Novatel RT-20 differential GPS
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20-cm CEP real-time kinematic accuracy in
differential mode (RT-20)
“on-the-fly” initialization
5 Hz RT-20 position maximum output rate
L1 C/A code
12 channel “all in view” parallel tracking
RS-232 connection
System Set-up
INS - to replace MAPS
Honeywell
HG1700AG11
IMU



Vx
Vy
Vz
SBC
Primary
100 Hz
KF
Align/Calib
Nav Sol
Primary CPU
Lat
Lon
Alt



Vn
Ve
Vd
20 Hz
PC104
Secondary
KF
Novatel RT-20
Secondary CPU
GPS
KF
Time
Lat
Lon
Alt
1-5 Hz
Time
Lat
Lon
Alt



Vn
Ve
Vd
10-15 Hz
To
MCU
Loosely Integrated System
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KF-driving-KF set-up
Advantages
– low-level modularity (use different inertial sensors)
– ability to directly compare systems by mix-matching
components (MAPS/Ashtech vs IMU/Novatel)
– faster development time
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Disadvantages
– more difficult to tune both filters since one affects the
other
– need more computing power
– more expensive
Inertial Navigation System (INS)
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Inputs
– raw inertial data from IMU
– initial conditions for alignment (initial position from
secondary CPU, initial accelerations from IMU)
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Processes
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calibration (correctly interpret output of sensors)
alignment (initial position, velocity and attitude [PVA])
IMU data reception & averaging (from 100 Hz to 20 Hz)
navigation solution (current PVA at 20 Hz)
primary KF (smoothing through data loss)
Outputs
– current PVA at 20 Hz in Local Geodetic Vehicle (LGV)
coordinates
Primary CPU Software Setup
Using DOS
and DMA
20 Hz
To PROCMAN
of Secondary CPU
HOSTCOM
20 Hz
Primary KF
20 Hz
Alignment
Nav Sol
20 Hz
Calibration
IMU Com
Primary CPU Software Setup
Using Lynx OS
and data polling
20 Hz
To PROCMAN
of Secondary CPU
HOSTCOM
PROCMAN
600 Hz
20 Hz
20 Hz
IMU Com
Calibration
Align
Primary KF
Nav Sol
IMU Data Processing
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ACB-104 serial communications card set-up to read in
SDLC messages on RS-422 interface line
Use Direct Memory Access (DMA) to read in data at 1 MHz
(1 Mbps)
DMA driver running in DOS environment
DMA - During a DMA cycle, the DMA controller chip is
driving the system bus, transferring data to/from memory
from/to an I/O device, bypassing the CPU, thus freeing it up
for other functions
IMU data will be averaged from 100 Hz to 20 Hz, in order to
lessen processing power needed to output navigation
solution and KF corrected PVA data
Navigation Solution
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IMU input data (delta velocities and delta angles) are in
vehicle body coordinates
Input data also includes general and local gravity
components
Earth angular rotation rate is considered
WGS84 reference ellipsoid used to model earth
Inertial navigation is affected by Schuler frequency (time
required for one revolution around a circular orbit a
constant distance from the center of a spherical earth)
navigation solution computes present PVA data from past
values and converts them to LGV coordinates
navigation solution becomes model for primary KF
Inertial Navigation
YL
 North
YL
 North
N = Nav -Frame
(XL, YL, ZL)
Y aw
V ehic le Centerline
P rojec tion onto
Level P lane
P S IC
XB = Nose
XL
XL
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E as t
YB = Right W ing
(Z L = Up)
E as t
(Z L = Up)
E as t
B = Body-Frame
(XB, Y B, Z B)
Platform Heading = PSIC
= PSIC -
ZB = Belly
(Lat, Lon, Alt) = Position
A

HG1700
IMU
Navigation
Processor
Vn
 n
100 Hz
Lat(0), Lon(0), Alt(0)
Initial
Conditions
- Align Mode
- Nav Mode
(VX, VY, VZ) = Velocity
( , , ) = Euler Angles
Speed, Heading, Range, etc
, ... (other parameters)
IMU/GPS Integration
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Inputs
– current PVA at 20 Hz from INS
– current position (LGV) and time from DGPS at 1 Hz
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Processes
– secondary KF performs smoothing through GPS loss
– secondary KF also performs error bounding by
constantly updating navigation solution with accurate
GPS position data, thus eliminating IMU drift and need
for Zero Velocity Update (Zupt)
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Outputs
– ships out POS messages to MCU at 10-15 Hz
Secondary CPU Software Setup
To MCU
10-15 Hz
HOSTCOM
PROCMAN
20 Hz
10-15 Hz
1-5 Hz
INS Com
GPS Com
Secondary KF
Extended Kalman Filter
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Estimator / Predictor
Evaluates a estimated trajectory close to the
actual trajectory using updated system variables
Define an State Error Vector
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velocity errors
position errors
attitude errors
accelerometer & gyro calibration coeff
gravity
Propagate incremental and total state vector
across each integration step
IMU/GPS POS shelf
IMU
PC104
Freewave
radio
Novatel
RT-20
DC-DC
converter
MAPS/GPS POS shelf
Ashtech Z-12
GPS receiver
Honeywell
MAPS
PC104
Freewave
radio
NTV GPS Antenna Set-up
GPS Base Station Setup
IMU/GPS vs MAPS/GPS
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Translate IMU/GPS position to MAPS/GPS reference
point on ATV (mule)
Test under ideal conditions
– solid GPS satellite lock and radio link at all times
– autonomous survey from 1-2 hours
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Test under adverse conditions
– temporarily withhold GPS data at specific areas on the field
– completely withhold GPS data
– manually introduce erroneous GPS data
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Position data will be compared against postprocessed data from Ashtech receiver
Typical Comparison Survey
Area A
* arrows indicatdirection of sweep
Typical INS (MAPS) Drift
GPS Position Convergence
System Comparison
MAPS/GPS
7 cm
IMU/GPS
20 cm
Orientation accuracy
0.01 deg
0.05 deg
Velocity accuracy
0.001 m/s
0.005 m/s
Data Rate
10 Hz
15 Hz
Align time
8-10 min
TBD
Position accuracy (CEP)
Dimensions (L x W x H)
Weight
Price
0.7 x 0.8 x 0.6 m 0.7 x 0.8 x 0.2 m
~ 60 lbs
~ 15 lbs
$ 130,000
$ 40,000
Project Schedule
Aug
Sep
IMU Comm
Nav Sol / Align
Primary KF
GPS Integration
Testing
Final Report
To date finished
Projected completion
Oct Nov
Dec
Jan
Feb
Mar
Thank You