28-03-2017 masterclass mechatronics 4.0 - indoor and outdoor localisation and positioning - using...
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USING UWB TECHNOLOGY AND SENSOR FUSION FOR NAVIGATION OF AN AGV
Risang Yudanto
Flanders Make
Master Class Seminar ‘Indoor and Outdoor Positioning’
28 March 2017
2
Application case
Autonomous navigation of an agriculture AGV in a green house
Requirements:
1-2 Centimeter accuracy
Precise and smooth positioning
High update rate (>25 Hz)
GPS signal is not always available
Other technology is needed to localize the AGV
Visual beacon accurate but may suffer from environment (fogs, etc)
UWB positioning interesting, but still need to be validated
3
Ultra-Wide Band (UWB) Technology
UWB signals are typically modulated pulse train, with very short pulse duration (in the order of nanosecond, or sub-nanosecond)
• This time resolution leads to precise ranging capability
The very short pulse duration leads to large signal bandwidth
• Normally ≥ 500 MHz
Images source: I. G. Zafer Sahinoglu, Sinan Gezici. Ultra-wideband Positioning Systems: Theoretical Limits, Ranging Algorithms, and Protocols. Cambridge University Press, October 6, 2008.
4
Decawave UWB Technology
Frequency: 3.4 – 4.8 GHz and 6 – 8.5 GHz
Bandwidth 499.2 MHz or 900 MHz
Enables two-way UWB communication to measure range (Two-Way-Ranging TWR)
No synchronization is required
±10 cm ranging accuracy (bias error)
Max distance, outdoor line-of-sight:
200 m @ 110 kbps PHY data rate
60 m @ 6.8 Mbps PHY data rate
Tag Anchor
poll
response
final
report
5
UWB Localization Architecture using Two-Way-Ranging
Mobile platform
Tag
(x0,y0,z0) (x1,y1,z1)
(x3,y3,z3) (x2,y2,z2)
Anchor 1Anchor 0
Anchor 2Anchor 3
R1
R2R3
Processing Unit
R0
R0,R1,R2,R3
Visualization & configuration
interface
R0,R1,R2,R3
3x or more ToF (Ranges) 3D localization
6
Factors contributing to position error
Range measurement error (bias & random part)Non line-of-sight between tag and anchor(s)
Multipath signal
Internal source of error:Clock noise and clock drift in the receiver
Signal delay in the antenna
…
Dilution of Precision (DOP)Anchors configuration and tag relative position to the anchors
Direct signal
Multipath signal
7
DOP Concept
High Uncertainty
Low Uncertainty
Poor Geometry
(high DOP)
Good Geometry
(low DOP)
Tag
Tag
Anchor Anchor
Anchor Anchor
Anchor
Anchor
Anchor
Anchor
8
DOP & Position Error
DOP can be used to analyze the expected variation of position error of different anchors configurations of a localization algorithm under ideal condition (no multipath, no signal blocking). Anchor
Anchor
Anchor
AnchorUEREyxD
UEREzyxD
HDOP
PDOP
uu
uuu
222
2223
Ranging error
mUERE 1.0
9
Anchors configuration in the greenhouse
• Horizontal (XY) dilution of precision is ≤ 1.2 in most of covered area
Anchor Anchor
Anchor Anchor
• Anchors height: 0.385 m• Tag height: 0.88 m
AnchorAnchor
AnchorAnchor
Tag
10
Using only UWB for vehicle navigation is not enough
• Advantages
• No position drift over time
• No need for recalibration over time
• Accurate for long periods
• Disadvantages
• Low update rate
• Considerable system delay
• Not precise for short periodsnot smooth enough for controller
• Need for external infrastructure
UWBReference
UWBReference
11
Other sensors (IMU, encoders) have also their own advantages and disadvantages
• Advantages
• High update rate
• Limited system delay
• Precise for short periods
• No need for external infrastructure
• Disadvantages
• Position drift over time
• IMU sensitivity and offset drift
• IMU needs recalibration over time
• Not accurate for long periods
12
Combine UWB, Encoders and Inertial Measurement Unit for AGV Navigation
Low cost IMU (Accelerometer & Gyroscope)
Decawave anchor
Acceleration at tangential direction
Acceleration at normal direction
Decawave tag
Yaw rate
Wheel velocity (Left)
Wheel velocity (Right)
x
Orientation
y
13
Implementation with multi-rate Extended Kalman Filter
Measurements @ different rates:
• UWB positioning (position: x,y) • low rate: < 20 Hz
• Encoder (velocity: v) • high rate: 100 Hz
• IMU (angular rate: ω, acceleration: at, an)• high rate: 100 Hz
UWB positioningx, y
IMU Measurementsω, at, an
Sensor Fusion (EKF)
Low rate < 20 Hz High rate 100 Hz
Encoder Measurements vL, vR
x, y, θ, v, ω, at, an, aω
To controller
State estimate @ high rate
• Position: x, y
• Orientation: θ
• Linear velocity: v
• Angular rate: ω
• Acceleration: at, an, aω
14
Multi rate estimator
Low rate UWB
High rate IMU
Time
Non synchro: fused in the next sample time
High rate Encoder
System time
15
Hardware platform comparison for sensor fusion implementation
Zed-board
RPi 1 B+ RPi 2 B XMC 4500
Hercules STM32F7 SoM
Processor Cortex A9 Cortex ARM1176JZ
Cortex A7 Cortex M4F Cortex R4F Cortex M7F
Clock freq. 667 MHz 700 MHz 900 MHz 120 MHz 220 MHz 216 MHz
Floating pt. Yes Yes Yes Yes Yes Yes
Multicore 2 cores 1 core 4 cores 1 core 1 core 1 core
DMIPS/core 1667 875 1710 150 356 462
RAM 512 MB(?) 512 MB 1 GB 128 kB 256 kB 512 kB
I/O ?x SPIEthernet
3(?)x SPIEthernet
3(?)x SPIEthernet
4(?)x SPIEthernet
?x SPI Ethernet
2 x SPI Ethernet
Form factor PCB PCB9 x 6 cm
PCB9 x 6 cm
PCB PCB PCB (in developmen
t in FM)
Developmentenvironment & tools
Xilinx tools Linux Linux Eclipse, debugger
Code Composer
Studio
Eclipse, debugger
Module price(EUR)
435 30 30 30 200 From 27 USD
16
Experimental validation on the AGV prototype
1σ : 0.0105 - 0.0175 [m]
Some signal drops
17
Experimental validation - AGV Trajectory
• The fusion output is smooth enough forthe controller
• Position difference to reference < 20 cm
Anchor
Anchor
Anchor
Anchor
18
Positioning without systematic ranging error (simulation)
• True position is within thedistribution of the estimates
Anchor Anchor
Anchor Anchor
• Ranging error 1σ: 0.0175 [m] • Ranging error mean: 0
19
Positioning with systematic ranging error (simulation)
• True position is outside thedistribution of the estimates
Anchor Anchor
Anchor Anchor
• Ranging error 1σ: 0.0175 [m] • Ranging error mean: +0.1 [m]
20
Conclusions
A low-cost localization system for autonomous navigation of agriculture AGV has been developed
Fusion of UWB positioning system, encoders and inertial measurement unit
It has been implemented on low cost embedded platform and validated on a prototype of agriculture AGV
The sensor fusion improves positioning precision and gives other information important for AGV navigation such as orientation, velocity, angular rate and acceleration
Sensor fusion with EKF, however, doesn’t entirely remove bias error
21
Vestiging Lommel:
Oude Diestersebaan 133
3920 Lommel
Belgium
Tel. +32 11 790 590
Fax +32 11 790 591
info@flandersmake.be
Vestiging Leuven
Campus Arenberg
Celestijnenlaan 300 - bus 4027
B-3001 Heverlee
Tel.: +32 16 32 80 50
Fax: +32 16 32 80 64
info@flandersmake.be
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