multi-level soil sensing systems to identify safe...
TRANSCRIPT
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MULTI-LEVEL SOIL SENSING SYSTEMS TO
IDENTIFY SAFE TRAFFICABILITY AREAS FOR EXTRA-PLANETARY ROVERS
Francisco Comin
May, 16th 2013
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Context and Motivation
MISSIONS
•MSL
•MER
•PATHFINDER
OBJECTIVES
•Climate and geology
•Human exploration
•Life on Mars?
Da
y N
igh
t
FAST
SAFE
Source: NASA
Source: NASA
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PRIMARY ROVER
• EXOMARS test bed
• Mission-critical
• Wheeled and heavy
SCOUT ROVER
• DFKI Prototype
• Terrain characterisation
• Mobile and lightweight
Mission Concept
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Soil Sensor Systems
• Soil sensor sub-systems and data fusion
PRIMARY ROVER
Remote
Sensing
DATA FUSION
STAGE 1
Wheeled-Bevameter
Or
PathBeater
DATA FUSION STAGE 2
NAVIGATION SYSTEM
SCOUT ROVER
Wheel-Leg
Soil
Interaction
Ground
Penetrating
Radar
Dynamic
Plate
Dynamic
Cone
Penetrometer
Outputs
GO MAYBE NO-GO
% TRAFF.
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• Soil sensors deployment and detection properties
Soil Sensor Systems
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Replicate pressure footprint
► Safety margin for low sinkage
► Maximum sinkage of 75mm
Wheel-Leg-Soil Interactions (UoS)
• Load Testing Foot (LTF)
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Wheel-Leg-Soil Interactions (UoS)
• Sensor Components and Function
Output Shaft Encoder
► Absolute angular position
► Angular speed
Current Transducer
► Motor current consumption
Inertial Measurement Unit
► 3-axis linear accelerations
► 3-axis rotation rates
Belly Camera
► Wheel-leg terrain interface images
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Wheel-Leg-Soil Interactions (UoS)
• Single wheel-leg lab testing and raw data acquisiton
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Colour segmentation (blue) and blob detection
Masking of the area of interest
Sinkage measurement from wheel-leg hub to blob edge
Wheel-Leg-Soil Interactions (UoS)
• Vision-based sinkage detection
(1)
(2)
(3)
(4)
Shadows
Noise
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Layers of materials with different properties
Discriminate soil type and layer thicknesses
Detect subsurface voids
Ground Penetrating Radar (UoS)
• GPR Simulations
Source: Cobham PLC Source: Cobham PLC
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Hybrid Dynamic Plate / Cone (UoS)
IMU
• Hybrid Actuation Mechanism
Low mass of scout
requires dynamic impact
to generate desired force
Common drive motor to
save payload space and
mass
Dual-mode to adjust
impact force through
spring pre-load
Coupling mechanism
► Coupled for plate
► Un-coupled for cone
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Selection of appropriate impact forces
Tests with three plate configurations
► Solid
► With Hole
► With Cone
Hybrid Dynamic Plate / Cone (UoS)
• Manual Drop Mass Tests
SSC-2
ES-3
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Clearer differentiation in initial blows
Asymptotic trend for higher blow number
No significant differences between plate configurations
Hybrid Dynamic Plate / Cone (UoS)
0
1
2
3
4
5
6
7
8
9
10
0 1 2 3 4 5 6
Dep
th p
er
Blo
w (
mm
)
Blows
• Plate Tests Results
Tests on ES-3
Solid Plate
Plate with Hole
Plate with Cone
Marker shape (Plate Configuration)
Loose Preparation
Medium Preparation
Dense Preparation
Marker colour (Density Preparation)
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First two blows discriminate different soil preparations
Asymptotic trend for further blows
Steepness of curve also reveals soil characteristics
Hybrid Dynamic Plate / Cone (UoS)
0
10
20
30
40
50
60
70
0 2 4 6 8 10
Sin
kag
e (
mm
)
Number of Blows
ES-3 - Sinkage per blow (mm)
0
10
20
30
40
50
60
70
0 2 4 6 8 10
Sin
kag
e (
mm
)
Number of blows
SSC-2 - Sinkage per blow (mm)
• Cone Tests Results
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Passive wheel with downward force
Four-bar mechanism allows vertical range of movement
No-Brake operation
► Encoder measures wheel rotation Ground speed/Slip estimates
► Slip, sinkage and vertical force Load bearing Bekker parameters
Full-Brake operation
► Triggered periodically in time or traversed distance
► Slip and horizontal force Shear strength Bekker parameters
Wheeled Bevameter (LSG)
• Operating Principle
No-Brake
Operation
Full-Brake
Operation
Periodically Normally
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Edge mounted to lie on wheel path
Hinge actuator to change between stowed and deployed
Release/lock actuator for the four-bar mechanism
Wheeled Bevameter (LSG)
Stowed Position Deployed Position
• Deployment
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Slope compliance
Obstacle impact damping
Automated stall detection
Wheeled Bevameter (LSG)
• Mechanical mock-up testing
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Two long arms with a pyramidal cone tip at their ends
Stow for safety in case of steep slopes or obstacles
Load Bearing Test
► Whipping motion of arm, impact of cone on the soil
► Impact forces and penetration measured by an IMU
Shear Strength Test
► Short driving with cone in the soil
► Resistance force measure in arm deflection by strain gauges
PathBeater (LSG)
• Operating Principle
Safety
Check
Load Bearing
Test
Unsafe Shear Strength
Test
Safe
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One arm mounted on each edge
Arms lie over wheel paths in deployed position
Spring-loaded whipping actuation
PathBeater (LSG)
• Deployment
Stowed Position
Deployed Position
Actuated Position
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PathBeater (LSG)
• Slope Considerations
Steep slope or obstacle detection to avoid damage
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PathBeater (LSG)
• Free fall and penetration tests
Free fall tests with different masses and cone angles
Automated penetration tests with sensor data acquisition
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Conclusions
Collaborative mission concept for safer and faster navigation
High-mobility scout dedicated to terrain characterisation
Development of sensors with overlapping areas of detection:
► Combine their terrain characterisation properties
► Redundancy in detection for increased robustness
Multi-level sequential deployment with increasing reliability:
► Reduce power consumption
► Minimise stopping time of the Scout rover
Sensors usable jointly/separately in other mission concepts
Initial testing of the different sensor systems in lab conditions
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Thanks for your attention!
Scout Rover Sensors
William A. Lewinger (UoS) e-mail: [email protected]
Francisco Comin (UoS) e-mail: [email protected]
Marcus Matthews (UoS) e-mail: [email protected]
Sinkage Detection
Said Al-Milli (UoS) e-mail: [email protected]
Conrad Spiteri (UoS) e-mail: [email protected]
Yang Gao (UoS) e-mail: [email protected]
Wheeled Bevameter
Lutz Richter (LSG) e-mail: [email protected]
PathBeater
Stephen Ransom (LSG) e-mail: [email protected]
Technical Manager
Chakravarthini Saaj (UoS) e-mail: [email protected]