imu gpsppt - IMU GPS Positioning System

Document Sample
imu gpsppt - IMU  GPS Positioning System Powered By Docstoc
					IMU / GPS Positioning System

     Center for Intelligent Machines and Robotics

     Rommel E. Mandapat
    Project Goals
 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
 The system performance of the IMU/GPS will
  be evaluated against that of the existing
Motivation & Approach
   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
   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
 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
 Inertial message output at 100 Hz (, , ,
  Vx, Vy, Vz)
 1 MHz output clock rate
Novatel RT-20 differential GPS
   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                                    Lat
HG1700AG11                    SBC             Lon
                                            Alt
                                                    20 Hz   PC104           Time
 IMU              100 Hz
                                KF                                           Lat
                              Align/Calib                                   Lon
             Vy                                              Secondary
                               Nav Sol        Vn                              Alt   10-15 Hz    To
                             Primary CPU      Ve                KF             
    Novatel RT-20                                                             
                                                             Secondary CPU
                              Time                                            Vd
              KF               Lat          1-5 Hz
   GPS                        Lon
Loosely Integrated System
   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
   Disadvantages
    – more difficult to tune both filters since one affects the
    – need more computing power
    – more expensive
Inertial Navigation System (INS)
   Inputs
    – raw inertial data from IMU
    – initial conditions for alignment (initial position from
      secondary CPU, initial accelerations from IMU)
   Processes
    –   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)
Primary CPU Software Setup
                             To PROCMAN
 Using DOS        20 Hz      of Secondary CPU

 and DMA
                      20 Hz
                Primary KF
                      20 Hz
  Alignment      Nav Sol
                      20 Hz
  Calibration   IMU Com
 Primary CPU Software Setup
 Using Lynx OS                    To PROCMAN
 and data polling       20 Hz     of Secondary CPU


       600 Hz                                20 Hz
IMU Com                            20 Hz             Primary KF

         Calibration      Align          Nav Sol
IMU Data Processing
   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
   IMU input data (delta velocities and delta angles) are in
    vehicle body coordinates
   Input data also includes general and local gravity
   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-Fram e                                                                       Yaw
                    (XL, Y L, Z L)                                                                                             Vehicle Centerline
                                                                                                                                Projection onto
                                                               XB = Nose                                                          Level Plane

                               XL                                                                                             XL
                                                                                                                       
                               East                                                                                           East
  (ZL = Up)                                                YB = Right Wing          (ZL = Up)
                                      East                                                          Platform Heading = PSIC
                                                          B = Body-Frame                                   = PSIC - 
                                                            (X B, YB, ZB)

                                             ZB = Belly

                                                                                                        (Lat, Lon, Alt) = Position
                                                                                                          (VX, VY, VZ) = Velocity
  A                                           Vn                          Processor
                  HG1700                                                                                      ,
                                                                                                              ( , ) = Euler Angles
                                                              100 Hz
                  IMU                         n                         - Align Mode
                                                                           - Nav Mode                  Speed, Heading, Range, etc
                                              Lat(0), Lon(0), Alt(0)                                    , ... (other parameters)

IMU/GPS Integration
   Inputs
    – current PVA at 20 Hz from INS
    – current position (LGV) and time from DGPS at 1 Hz
   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)
   Outputs
    – ships out POS messages to MCU at 10-15 Hz
Secondary CPU Software Setup
                      To MCU
                      10-15 Hz


    20 Hz                    10-15 Hz
                1-5 Hz

INS Com     GPS Com        Secondary KF
Extended Kalman Filter
   Estimator / Predictor
   Evaluates a estimated trajectory close to the
    actual trajectory using updated system variables
   Define an State Error Vector
    –   velocity errors
    –   position errors
    –   attitude errors
    –   accelerometer & gyro calibration coeff
    –   gravity
   Propagate incremental and total state vector
    across each integration step


Freewave     RT-20


    Ashtech Z-12   PC104
    GPS receiver   Freewave

NTV GPS Antenna Set-up
GPS Base Station Setup
   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
   Test under adverse conditions
    – temporarily withhold GPS data at specific areas on the field
    – completely withhold GPS data
    – manually introduce erroneous GPS data
   Position data will be compared against post-
    processed data from Ashtech receiver
Typical Comparison Survey

   Area A

      * arrows indicatdirection of sweep
Typical INS (MAPS) Drift
GPS Position Convergence
System Comparison
                            MAPS/GPS            IMU/GPS
Position accuracy (CEP)       7 cm                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
Dimensions (L x W x H)    0.7 x 0.8 x 0.6 m 0.7 x 0.8 x 0.2 m
Weight                        ~ 60 lbs          ~ 15 lbs
Price                        $ 130,000          $ 40,000
 Project Schedule
                  Aug     Sep Oct Nov   Dec Jan Feb Mar
IMU Comm
Nav Sol / Align
Primary KF
GPS Integration
Final Report
          To date finished
          Projected completion
Thank You

Shared By: