dynamics simulation of rovers on soft terrain: modeling and experimental validation paper81845
DESCRIPTION
Ali Azimi(1,2), Daniel Holz(2), József Kövecses(1), Jorge Angeles(1), Marek Teichmann(2) 1 Department of Mechanical Engineering and Centre for Intelligent Machines, McGill University, Montreal, Canada 2 CM-Labs Simulations Inc., Montreal, CanadaTRANSCRIPT
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Dynamics Simulation of Rovers On Soft Terrain: Modeling and Experimental Validation
Ali Azimi1,2, Daniel Holz2,
, József Kövecses1, Jorge Angeles1, Marek Teichmann2
1 Department of Mechanical Engineering and Centre for Intelligent Machines, McGill University, Montreal, Canada
2 CM-Labs Simulations Inc., Montreal, Canada
ISTVS 7th Americas Regional Conference,
Tampa, Florida, USA, November , 2013
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2 Dynamics Simulation of Rovers On Soft Terrain 2 A. Azimi, D. Holz, J. Kövecses, J. Angeles, M. Teichmann
Purpose of our work:
Developing efficient model(s) for wheel-soil interaction compatible with multibody dynamics simulation environments (e.g. CMLabs’ Vortex)
In this presentation:
Novel framework for implementation of semi-empirical terramechanics models in multibody environments
Experimental verifications
Introduction
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3 Dynamics Simulation of Rovers On Soft Terrain 3 A. Azimi, D. Holz, J. Kövecses, J. Angeles, M. Teichmann
Semi-empirical Models
Scope: Steady-state operation
Shortcomings: No energy dissipation in vertical motion
Not suitable for transient operations
Undefined slip-ratio for a stationary wheel
At slow speed, abrupt changes to reaction forces stiff system
Common approach in the literature for dynamic simulation: Soil reaction as external forces/moments (explicit force)
Causes problems with undefined slip-ratio for a wheel stationary or at low speed
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4 Dynamics Simulation of Rovers On Soft Terrain 4 A. Azimi, D. Holz, J. Kövecses, J. Angeles, M. Teichmann
Developed Framework
A semi-empirical model provides normal and shear stress distributions (Bekker, 1956), (Wong and Reece, 1967), (Ishigami et al., 2007).
Summation of stresses gives soil reaction forces/moments
Normal force Fz
A viscoelastic system with variable stiffness and damping coefficients:
Other reactions ( Ft , Rc , and Trr )
By means of kinematic constraints with set-valued force laws, which can form a LCP (linear complementarity problem)
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5 Dynamics Simulation of Rovers On Soft Terrain 5 A. Azimi, D. Holz, J. Kövecses, J. Angeles, M. Teichmann
Developed Framework (continued…)
Traction force:
Resistance force:
Residual resistance torque:
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6 Dynamics Simulation of Rovers On Soft Terrain 6 A. Azimi, D. Holz, J. Kövecses, J. Angeles, M. Teichmann
Lateral Force
(shear) (Bulldozing)
Revised lateral force model:
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7 Dynamics Simulation of Rovers On Soft Terrain 7 A. Azimi, D. Holz, J. Kövecses, J. Angeles, M. Teichmann
LCP Formulation
Soil reaction as:
Mathematical model of an n-DOF system
can be represented as a Mixed LCP, defined by (details in Azimi 2013):
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8 Dynamics Simulation of Rovers On Soft Terrain 8 A. Azimi, D. Holz, J. Kövecses, J. Angeles, M. Teichmann
Mobility Prediction of Rovers on Soft Terrain
Analyze wheel—ground overlap: Examine “wheel footprint”
8 D. Holz, A. Azimi, M. Teichmann, J. Kövecses
Contact region is approximated by a (least-squares) plane
Cylinder/plane intersection
Sinkage estimation
Stable simulation
Active vertices are used to determine soil hardening and compaction
Irregular Terrains
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9 Dynamics Simulation of Rovers On Soft Terrain 9 A. Azimi, D. Holz, J. Kövecses, J. Angeles, M. Teichmann
Mobility Prediction of Rovers on Soft Terrain
Place contact constraints according to cylinder/plane inters.
Constraint are added for Rc, Ft,
Trr, and Fl
9 D. Holz, A. Azimi, M. Teichmann, J. Kövecses
zF
tFlF
cR
Irregular Terrains (continued…)
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10 Dynamics Simulation of Rovers On Soft Terrain 10 A. Azimi, D. Holz, J. Kövecses, J. Angeles, M. Teichmann
Soil Hardening and Compaction
Active vertices are used in determining soil hardening and compaction
Wheel sinkage
Pre
ssu
re
reloading
unloading
loading
Multi-pass model of Wong is adapted here
Normal stress ( ), as shown:
Shear stress( ): same relation as uncompacted soil:
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11 Dynamics Simulation of Rovers On Soft Terrain 11 A. Azimi, D. Holz, J. Kövecses, J. Angeles, M. Teichmann
Experimental Verification: Juno Rover
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12 Dynamics Simulation of Rovers On Soft Terrain 12 A. Azimi, D. Holz, J. Kövecses, J. Angeles, M. Teichmann
Measurements
Juno rover measurements: Load cell: drawbar pull
Total station: rover position
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13 Dynamics Simulation of Rovers On Soft Terrain 13 A. Azimi, D. Holz, J. Kövecses, J. Angeles, M. Teichmann
Experimental Verification: Juno Rover
Drawbar pull experiments:
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14 Dynamics Simulation of Rovers On Soft Terrain 14 A. Azimi, D. Holz, J. Kövecses, J. Angeles, M. Teichmann
Experimental Verification: Juno Rover
Drawbar pull experiments with added mass:
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15 Dynamics Simulation of Rovers On Soft Terrain 15 A. Azimi, D. Holz, J. Kövecses, J. Angeles, M. Teichmann
Juno Experiments: Irregular Terrain
LIDAR Scan
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16 Dynamics Simulation of Rovers On Soft Terrain 16 A. Azimi, D. Holz, J. Kövecses, J. Angeles, M. Teichmann
Juno Rover Simulation in Vortex
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17 Dynamics Simulation of Rovers On Soft Terrain 17 A. Azimi, D. Holz, J. Kövecses, J. Angeles, M. Teichmann
Juno Experiments: Irregular Terrain
Motor speed from experiment used as input in simulation
Results from the Wong-Reece-Ishigami model with our framework:
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18 Dynamics Simulation of Rovers On Soft Terrain 18 A. Azimi, D. Holz, J. Kövecses, J. Angeles, M. Teichmann
Conclusions
Developing a framework for implementation of semi-empirical terramechanics models in a multi-body dynamics environment
Computationally efficient: The interaction is modelled via using kinematic constraints with set-valued force laws. With that, the problem was formulated as LCP.
Various forms of semi-empirical Bekker models can be incorporated
Operation on irregular terrain with soil compaction and hardening in a stable way
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19 Dynamics Simulation of Rovers On Soft Terrain 19 A. Azimi, D. Holz, J. Kövecses, J. Angeles, M. Teichmann
Multipass Soil Compaction Model