Abstract-Future planetary exploration missions will require wheeled mobile robots ("rovers") to traverse very rough terrain with limited human supervision. Wheel-terrain interaction plays a critical role in rough-terrain mobility. In this paper, an online estimation method that identifies key terrain parameters using on-board robot sensors is presented. These parameters can be used for traversability prediction or in a traction control algorithm to improve robot mobility and to plan safe action plans for autonomous systems. Terrain parameters are also valuable indicators of planetary surface soil composition. The algorithm relies on a simplified form of classical terramechanics equations and uses a linear-least squares method to compute terrain parameters in real time. Simulation and experimental results show that the terrain estimation algorithm can accurately and efficiently identify key terrain parameters for various soil types.Index Terms-Mobile robots, planetary rovers, rough terrain, wheel-terrain interaction.

Future planetary exploration missions will require rovers to traverse very rough terrain with limited human supervision. Wheel-terrain interaction plays a critical role in rough-terrain mobility. In this paper an on-line estimation method that identifies key terrain parameters using on-board rover sensors is presented. These parameters can be used for accurate traversability prediction or in a traction control algorithm. These parameters are also valuable indicators of planetary surface soil composition. Simulation and experimental results show that the terrain estimation algorithm can accurately and efficiently identify key terrain parameters for loose sand. Introduction and Related WorkFuture planetary exploration missions will require rovers to perform challenging mobility tasks in rough terrain [S, 14, 161. Proposed future mission objectives include traversal of several kilometers with a high degree of autonomy. To accomplish these objectives, future control and planning methods must consider the physical characteristics of the rover and its environment, to fully utilize the rover's capabilities.Wheel-terrain interaction has been shown to play a critical role in rough-terrain mobility [l, 21. For example, a vehicle traversing loose sand has very different mobility characteristics than one traversing firm clay. For planetary rovers, it is desirable to estimate terrain parameters on-line, since on-line estimation would allow a rover to accurately predict the traversability of neighboring terrain regions.Terrain parameter estimation would also allow a rover to adapt its control and planning strategy to a given terrain [7]. Off-line (i.e. Earth-based) estimation could be performed, but the associated communication time delays are extensive. Finally, on-line terrain estimation is desirable for enhancing our understanding of planetary surface composition. *Department of Mechanical Engineering, BirZeit University Palestinian Territories Many researchers have studied methods for identifylng key wheel-terrain interaction model parameters [12, 151. Generally, these methods involve off-line estimation using costly, dedicated testing equipment. Terrain parameter estimation for a legged system has been documented in [3]. This approach uses an embedded three-axis force sensor, which most planetary rovers are not equipped with. Terrain parameter estimation for tracked vehicles has been proposed in [3]. This approach assumes a highly simplified "force coefficient" model of track-terrain interaction, which is not valid in deformable rough terrain.Parameter estimation of Martian soil has been performed by the Viking landers and the Sojourner rover [lo, 111. The Viking landers used manipulator arms to conduct trenching experiments. The Sojourner rover used the rover wheel as a bevameter-type device to identify soil cohesion and internal friction angle. Both missions used visual cues and off-line analysis techniques to compute soil parameters.In this paper, a method for on-line estimation of terrain cohesion and interna...

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In this contribution, a new closed form of a mathematical model of Nickel-Titanium (NiTi) shape memory alloy (SMA) and its thermo-mechanical wire hysteresis behavior is developed. The approach is based on experimental data. The behavior of the heated and naturally cooled wire is modeled by mathematical expression. The cycle of heating and cooling is performed under a constant load. The prediction of the hysteretic behavior is realized through models adaptation, as predetermination, or real time determination of the models values, is developed and presented in detail. Simulations for position control using PID controller is shown for comparison purposes. The developed approach is incorporated in a feed forward control scheme. A comparison between the actual position and the predicted models position shows promising results.Keywords SMA hysteric behavior · Hysteresis prediction of SMA wire · Real time modeling of SMA hysteresis · Testing and simulation of shape memory alloy phenomenological behavior

Abstract:The mobility of a planetary vehicle has numerous constraints imposed by the types of terrain.