1 Copyright © 2005 by ASME Proceedings of IMECE- 2005 2005 ASME International Mechanical Engineering Congress and Exposition November 5-11, 2005, Orlando, Florida, USA IMECE2005-79711 MEASURES FOR WHEEL SLIPPAGE AND SINKAGE DETECTION IN ROUGH-TERRAIN MOBILE ROBOTS Giulio Reina 1 , Lauro Ojeda 2 , Annalisa Milella 3 , and Johann Borenstein 4 1) University of Lecce Department of Innovation Engineering Via per Arnesano, Lecce, 73100 Italy 2, 4) University of Michigan Advanced Technologies Lab 1101 Beal Ave, Ann Arbor, MI 48108 3) Politecnico of Bari Department of Mechanical Engineering Via Japigia 182, Bari, 70125 Italy E-mail: 1 giulio.reina@unile.it , 2 lojeda@umich.edu , 3 milella@poliba.it , 4 johannb@umich.edu 1 Corresponding author. Submitted for review ABSTRACT Mobile robots are increasingly being used in high-risk, rough terrain situations, such as planetary exploration and military applications. Current control and localization algorithms are not well suited to rough terrain, since they generally do not consider the physical characteristics of the vehicle and of its environment. Poor attention has been devoted to the study of the dynamic ill-effects occurring at the wheel- terrain interface, such as slip and sinkage. These effects compromise odometry accuracy and traction performances leading to danger of entrapment with consequent mission failure. This paper describes methods for wheel slippage and sinkage detection aiming at improving vehicle mobility on highly challenging terrain. Novel measures for wheel slip detection are presented based on observing different sensor modalities implemented onboard and defining deterministic conditions for vehicle slippage. A vision-based algorithm for wheel sinkage estimation is also discussed based on edge detection strategy. Experimental results, obtained by a Mars rover-type robot operating in a rough-terrain environment, are presented. It is shown that these techniques are effective in detecting the dynamic effects due to wheel-terrain interaction and can lead to an efficient understanding of the vehicle physical behavior. 1 INTRODUCTION For mobile robots driving across soft soils, such as sand, loose dirt, or snow, it is critical that dynamic effects occurring at the wheel-terrain interface be taken into account. The most prevalent of these effects are wheel slipping and sinkage, which greatly affect a robot’s mobility. Current control and localization algorithms generally do not consider the physical characteristics of the vehicle and of its environment. Failure to understand these characteristics could lead to danger of entrapment, inaccurate rover position estimation, and poor traction performances. Field trials performed at the Jet Propulsion Lab (JPL) in Pasadena, California, using a terrestrial analog of the Mars Exploration Rovers have indicated that there is a great amount of slippage in the drive wheel during traversal of Mars-like terrain [1]. This precludes the use of conventional dead- reckoning techniques for navigation [2], since they are based on the assumptions that wheel revolutions can be translated into linear displacement relative to the ground. This assumption is only of limited validity on loose terrain. If one wheel slips, then the associated encoder will register wheel revolutions even though these revolutions do not correspond to a linear displacement of the wheel. Conversely, if one wheel skids, fewer encoder pulses will be produced. Thus, in order to function properly on rugged terrain, it is necessary to take into account vehicle-terrain dynamic effects such as slipping and skidding.