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Improving the Performance of Mobile Robots on Uneven Terrain

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Improving the Performance of Mobile Robots on Uneven Terrain

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    1. Improving the Performance of Mobile Robots on Uneven Terrain Joseph Auchter Dr. Carl Moore FAMU/FSU College of Engineering 5 October 2007

    2. Wheeled Mobile Robots Increasing interest in autonomous robots operating outdoors on difficult terrains

    3. Wheel Slip for Outdoor Robots All wheeled vehicles will slip on uneven terrain Two kinds of wheel slip: Dynamic: due to insufficient friction, terrain deformation, etc Kinematic: due to lack of an instantaneous center of rotation compatible with all wheels

    4. Why Slip Occurs on Uneven Terrain Example: Ideal Ackermann Steering:

    5. Why Slip Occurs on Uneven Terrain Ackermann Steering on Uneven Terrain:

    6. Problems Caused by Wheel Slip Decreased localization ability due to odometric (wheel encoder) error accumulating without bound Power wastage Reduced traction, terrain traversibility

    7. Wheel Slip: Example

    8. The Proposed Solution Concept by N. Chakraborty and Dr. A. Ghosal at the Indian Institute of Science (2003) Passive Variable Camber (PVC): Lateral tilting of wheels allows the robot to move on uneven terrain without kinematic slip

    9. Research Hypotheses PVC will significantly reduce kinematic slipping on uneven terrain PVC will allow the wheel or tire to maintain better contact with the ground, improving traction and reducing dynamic slip

    10. Kinematic Simulation of a WMR Uneven terrain Robot equipped with Passive Variable Camber (PVC) joints Traditional robot modeling is inadequate: Need a new, precise way to simulate wheels rolling over uneven ground

    11. Analogy Between WMRs and Robot Hands

    12. Simulation Concept Apply dextrous manipulator modeling techniques to a wheeled mobile robot system Allows us to precisely simulate the motion of the wheels on an uneven terrain

    13. 3-Wheeled Mobile Robot Model Front wheel is steered Rear two wheels have Passive Variable Camber (PVC) joints Robot moves on uneven terrain

    14. System Model The following ODEs describe the system:

    15. Robot Joint Velocities

    16. Surface Parameterizations

    17. Contact Variables Contact variables for one wheel: Grouped for all wheels: Velocities of the wheel relative to the ground:

    18. Rolling Contact Equations and Vc are related by Montanas1 equations of contact:

    19. Closure Constraints Robot / ground system is a hybrid series / parallel mechanism. There are three serial kinematic chains in parallel Closure constraints: each chain of coordinate transformations must end in the same frame ({P} in this case)

    20. Closure Constraints The closure constraints can be written in the form:

    21. Velocity Relationships Following Han2:

    22. Velocity Relationships Let c be the number of columns of JPc. The QR decomposition of JPc is:

    23. Velocity Relationships This is the constraint equation for the input velocities . To make use of this equation, take the QR decomposition again as follows:

    24. Velocity Relationships After some manipulation, we can write:

    25. System Model The following ODEs describe the system:

    26. Kinematic Simulation Results

    27. Kinematic Simulation Results

    28. Simulation Results (Hill Climbing)

    29. Simulation Results (Hill Climbing)

    30. Simulation Results (Random Terrain)

    31. Simulation Results (Random Terrain)

    32. Simulation Results (Random Terrain)

    33. Next Steps Design and construct experimental test-bed Show that a wheel with Passive Variable Camber can roll over an uneven terrain without kinematic slip Investigate effects of PVC on power consumption and dynamic slip

    34. Supplementary Slides

    35. Template Template

    36. Effects of Wheel Slip: Example Huntsberger, et al (2002): long-range rover autonomy Application to NASAs Spirit and Opportunity Mars rovers Fuse odometry, gyros, and sun sensor with EKF to perform long-range (100s of meters) navigation Found ~15% error in odometry over test run Reported wheel slip resulting in increased power consumption

    37. Research Hypotheses PVC will improve robot self-localization Nearly all path-planning, map building, and navigation algorithms need good localization Localization especially tricky for outdoor robots on uneven terrain Wheel slippage very difficult to model and detect GPS alone not adequate multi-sensor fusion is necessary, usually including wheel odometry

    38. Research Hypotheses PVC will also reduce power consumption Power is costly: battery-operated, planetary exploration, long-term autonomous navigation

    39. Validation of PVC Hypotheses Kinematic simulation of a wheeled mobile robot (WMR) will determine whether PVC can eliminate kinematic slip Experimental test bed to show that a wheel with a PVC joint can roll on an uneven terrain without slip

    40. Summary: The Proposed Solution Passive Variable Camber (PVC) is introduced to reduce slip for wheeled mobile robots

    41. Summary: PVC Passive Variable Camber has the potential to provide strong benefits to outdoor mobile robots: Power efficiency Increased localization ability More effective path planning and obstacle avoidance Better traction on extreme terrains

    42. 3-Wheeled Mobile Robot Model

    43. Template Template

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