sensing and actuation for polar mobile robot

University of Kansas

Sensing and Actuation for Polar Mobile Robot

Eric L. Akers, Hans P. Harmon, Richard S. Stansbury (Presenter), and Arvin Agah

ITTC, University of KansasSeptember 20, 2004


Overview

• Introduction• Mobile Platform• Virtual Prototyping• Software• Computing and Connectivity• Sensors• Actuation• Evaluation


Introduction

• Polar Radar for Ice Sheet Measurement (PRISM)• Measurement of ice sheet properties in polar environments

• Mobile robot to aid data collection• Transports radar equipment

• Tows antenna array

• Precise movement for data collection

• Environmental challenges:

– cold temperatures, harsh winds, blowing snow.


Mobile Platform

• Requirements:• Operation at -30 degrees C to 40 degrees C.

• Operate at altitudes from 0m to 3000m above sea level.

• Transport 300kg of equipment.

• Support 40U’s of rack-mount space.

• Max ATV Buffalo• Six-wheeled ATV with optional tracks

• Amphibious (sealed)

• Protective enclosure designed and constructed

• Tank-like skid steering.


Mobile Platform – Max ATV Buffalo


Virtual Prototyping

• MSC.visualNastran• 3D simulation package.

• Evaluation of design parameters and rover performance:• Payload placement

• Wheels vs. Tracks

• Turning radius.

• Maximum climbable slope.


Virtual Prototyping

Virtual Prototype of PRISM Rover


Software:

• JAVA:• Portability.

• Object oriented design.

• PRISM Robot API• Interfaces for robot components.

• Events and Event Listeners

– Forward data updates.

– Propagate error notification

• Sensor and actuator drivers:• Instantiate API defined components.

• Utilizes manufacturers’ proprietary communication languages.


Computing and Connectivity

• RS-232 to USB Hub• Supports up to 16 sensors and Actuators

• 16-Port Switch• Connects onboard computers

• GoBook Max Ruggedized Laptop• Pentium III 750 MHz running Windows XP

• Operates at -30 degrees C.

• Shock-mounted hard drives.

• Waterproof


Sensors Requirements

• Task:• Centimeter-level position accuracy.

• Video for remote operation and outreach.

• Environmental:• Survive in polar environment.

• Determine weather conditions

• Detect and avoid human-made and naturally-occurring obstacles

• Proprioception• Current state: heading, position, orientation.

• Internal temperature

• Fuel level


Sensor Suite

• Global Positioning: • Topcon’s Legacy-E RTK GPS System

• Obstacle Detection:• SICK LMS221 Laser Range Finder

• Tilt and Temperature:• PNI Corp. TCM2-50


Sensor Suite

• Heading:• BEI Systron-Donner MotionPak II Gyroscope

• Weather:• Rainwise WS-2000 Weather Station

• Vision:• Pelco Esprit pan/tilt/zoom camera


Sensors – Hardware Integration

External Sensors


Sensors - Hardware Integration

Internal Sensors


Actuation:

• Three components to control:• Left and right brake.

• Throttle

• Linear actuators:• Electromagnetic motors.

• No gears.

• 20 μm resolution

• Controlled by microcontroller with RS-232 interface


Evaluation:

• Field experimentation:• Greenland 2003 – North GRIP Camp

– Individual sensor tests and data collection

• Greenland 2004 – Summit Camp

– Integrated tests with radar system.

• Climate Survivability:• Sensors operated in polar environment.

• Rover would become stuck occasionally when turning in soft snow.

• Batteries drained quickly and were replaced with power supplies.


Evaluation

• GPS Relative Accuracy:• Measured distance between two points vs. known distance

• Relative Accuracy:

x = 0.006 ± 0.004 meters

y = 0.010 ± 0.007 meters

z = 0.022 ± 0.016 meters


Evaluation• GPS Visibility:

• Measured number of GPS and GLONASS satellites available at the North Grip camp for a 24-hour period.


Evaluation

Obstacle Image vs. LMS221 Image: Snowmobile


Evaluation

Obstacle Image vs. LMS221 Image: Sastrugi


Evaluation

• Waypoint Navigation• Demonstrates the integration of sensors, actuation, and platform.

• Waypoints assigned in a pattern similar to its data collection pattern on the ice.

• Thresholds

– Waypoint arrival: 1 meter

– Heading on target: 10 degrees


Evaluation


Future Work:

• Additional fault tolerance.• Tighten waypoint path for greater accuracy.• Reduce rover payload to improve performance in

soft snow.• Additional field experiments in Greenland and

Antarctica.


Conclusion

• Mobile robot constructed for collection of radar data in polar regions.

• Robust suite of sensors was selected.• Vehicle automation has been developed and verified

using waypoint navigation.


Acknowledgements

• This work was supported by the National Science Foundation (grant #OPP-0122520), the National Aeronautics and Space Administration (grants #NAG5-12659 and NAG5-12980), the Kansas Technology Enterprise Corporation, and the University of Kansas.

sensing and actuation for polar mobile robot

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