Research: Autonomous Navigation with Stereo and Laser Perception

Stewart Moorehead

Current Status

The autonomous navigation system on Nomad has undergone significant improvements over its implementation in the Atacama Desert last year. The stereo cameras have been equipped with auto iris lenses that significantly reduce setup time and allow the robot to function in changing light conditions. The change in lenses was accompanied by changes in the camera calibration procedures. A single line laser scanner has also been added. The laser has two purposes: to detect holes or negative height obstacles which stereo cannot see, and to spot any other obstacles which stereo might miss. The laser has been seamlessly integrated into the navigation system using the new goodness map representation. The goodness map is another addition to Nomad. Each sensor takes its data and creates a map where each cell contains a goodness value, how good it is for the robot to be in that position, and a certainty, the sensor's belief in the data. These maps are then passed to morphin, which merges the maps and plans which direction to travel to maximize goodness. This methodology allows for the easy addition of sensors, but more importantly the goodness value may refer to something other than terrain ability such as science value, solar availability, etc. The final major change to the navigation system is a primitive form of error detection and recovery. This process monitors various signals and determines when the robot is in trouble. Currently it has two functions. It determines when the robot is stuck too close to an object to turn away. It also monitors motor currents and angle sensors to determine if the robot is driving on dangerous ground. This second, referred to as blind driving, is very important in Antarctica where the functionality of stereo and laser on ice fields is not known. Both monitors call a backup and turn maneuver to recover from the problem.

The navigation system has been tested in Pittsburgh. The backup maneuver has been tested, both when morphin and the blind driving modes have been active. Morphin, with the goodness maps, has been successfully tested with stereo as the only sensor as well as with laser as the only sensor running.

Goals

The immediate future calls for exhaustive testing in Antarctica. As a project demonstration the autonomous navigation system will be run under various polar conditions. Performance will be evaluated on the four major terrain types present at Patriot Hills: blue ice field, snow, moraine (large glacial rock deposits) and sastruggi (hardened snow hills). Of particular importance will be the testing of the stereo vision and laser sensors on these terrain types. The effects of and need for filters, particularly polarizing, on the stereo cameras will be a major part of this testing, and performed in cooperation with the French research laboratory LAAS. The navigation system will also be capable of driving blind if the sensors should prove ineffective.

After return from Antarctica, the navigation group will focus on three areas of research. First, the data collected in Antarctica will be examined thoroughly. This will provide a greater understanding of the terrain and environmental conditions which a future meteorobot will encounter and guide our development. Second, the method used to create a terrain map from stereo data will be improved. The current method of fitting planes to the data has difficulty detecting some obstacles quickly. A method employing fitting wavelets to the data will be examined. The third area of research will be to expand the error monitoring system to detect more faults, including some mechanical failures.
 
Find out about the autonomous traversal of polar terrain demonstration in the current Antarctic expedition.

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Robotic Search for Antarctic Meteorites 1998
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