Provisions for specification of hazards faced by a robotic vehicle (rover) equipped with a rocker-bogie suspension, for prediction of collisions between the vehicle and the hazards, and for simulation of poses of the vehicle at selected positions on the terrain have been incorporated into software that simulates the movements of the vehicle on planned paths across the terrain. The software in question is that of the Web Interface for Telescience (WITS), selected aspects of which have been described in a number of prior NASA Tech Briefs articles. To recapitulate: The WITS is a system of computer software that enables scientists, located at geographically dispersed computer terminals connected to the World Wide Web, to command instrumented robotic vehicles (rovers) during exploration of Mars and perhaps eventually of other planets. The WITS also has potential for adaptation to terrestrial use in telerobotics and other applications that involve computer-based remote monitoring, supervision, control, and planning.

This Computer-Generated Image is typical of the images generated in simulations of the articulation of the rocker bogies and the tilt of the main body of the rover as it traverses terrain.

The hazard-specification provision enables a user to interactively specify hazards in terms of zones on the terrain. On an interactive computer display that contains an overhead view synthesized from previously acquired images of the terrain, the user specifies the horizontal location of the center of a hazard zone. Then, using a display denoted a hazard window, the user specifies the height of the center of the hazard zone and the horizontal radius of the hazard zone. The user can also add a textual comment about the hazard. Once the hazard zone has been thus specified, it is depicted as a yellow circle on WITS synthetic views of the terrain.

The collision-prediction provision enables a user to see where the planned rover path could cause the rover to collide with a specified hazard. The traversal of the terrain by the rover is specified by designating way points, and the planned path becomes a sequence of straight-line (as viewed from overhead) segments between the way points. At small increments of position along the planned path, the distance from the rover to all the specified hazard zones is computed. The difference between each such distance and the radius of the hazard zone is computed and compared with two previously specified distances: one denoted the safe distance and a smaller one denoted the collision distance. If the computed difference distance exceeds the safe distance, then there is assumed to be no risk of collision and the affected segment of the path is shown green on the WITS synthetic terrain images. If the computed difference distance lies between the safety and collision distances, the affected path segment is deemed to be risky and is shown yellow on the terrain images. If the computed difference distance is less than the collision distance, the affected path segment is designated as a collision segment and is displayed in red.

The pose-simulation provision is, more specifically, a provision for simulating the articulation of the rocker-bogie portions of the suspension and the tilt of the main body of the vehicle, given the equivalent of a topographical map of the local terrain with which the vehicle is in contact (see figure). This provision enables the user to view the changing rover bogie angles as the rover travels its planned path across the terrain. For each increment of position along the path, the horizontal positions of the six rover wheels are computed approximately under the assumption that the rover tilt angles are small. Then the elevations of the wheels are computed by use of the estimated horizontal wheel coordinates and the topographical information. Then the bogey angles and the tilt angles of the main body are determined from the elevations of the wheels and the known geometric relationships among the wheels, the bogies, and the main body.

This work was done by Paul Backes, Jeffrey Norris, and Mark Powell of Caltech and Gregory Tharp of IA Tech, Inc., for NASA's Jet Propulsion Laboratory.

NPO-30450

Topics:
Autonomous vehicles Computer software and hardware Education and training Hazards and emergency operations Mechanical Components People and personalities Simulators Spacecraft Suspension systems Terrain Unmanned ground vehicles Vehicles
This Brief includes a Technical Support Package (TSP).
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Simulation of Hazards and Poses for a Rocker-Bogie Rover

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NASA Tech Briefs Magazine

This article first appeared in the February, 2004 issue of NASA Tech Briefs Magazine (Vol. 28 No. 2).

Read more articles from the archives here.

Overview

The document outlines advancements in hazard specification, collision prediction, and rover articulation simulation for rocker-bogie rovers, developed by the Jet Propulsion Laboratory (JPL) and presented in a NASA Tech Brief. These technologies are integrated into the Web Interface for Telescience (WITS), which allows remote operation of robotic vehicles during planetary exploration, particularly on Mars.

The primary focus of the document is on three key components:

  1. Hazard Zone Specification: This feature enables operators to interactively define hazard zones on the terrain that the rover should avoid. Users can specify the 3D center of a hazard zone by selecting a point in an overhead view and adjusting the height in a Synthetic Location window. The hazard zone is represented as a yellow circle on the WITS display, allowing for clear visualization of areas that pose risks to the rover.

  2. Hazard Collision Prediction: This capability assesses the planned rover path against specified hazard zones to predict potential collisions. Operators designate waypoints for the rover's traverse, and the software computes the distance from the rover to the center of each hazard zone at various points along the path. The path is color-coded based on safety assessments: green for safe segments, yellow for risky segments, and red for collision areas. This predictive analysis helps operators make informed decisions about rover navigation.

  3. Rover Bogie Articulation Simulation: This simulation allows for the visualization of the rover's movements and the changing angles of its bogies as it traverses different terrains. Understanding how the rover will articulate in response to the terrain is crucial for planning effective traverses and ensuring the rover's stability and safety.

The document emphasizes the importance of these technologies in enhancing the planning and execution of rover missions. By allowing operators to specify hazards, predict collisions, and simulate rover movements, the WITS system significantly improves the safety and efficiency of rover operations on Mars and has potential applications in terrestrial telerobotics.

Overall, the advancements described in the document represent a significant step forward in robotic exploration, enabling more sophisticated and safer navigation of challenging terrains. The successful implementation of these technologies in field tests demonstrates their effectiveness and potential for future missions.