DYNAMICS AND NAVIGATION CONTROL OF PLANETARY EXPLORATION ROVERS

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The goal of this research is to investigate the motion dynamics and navigation control methods for planetary exploration rovers that negotiate natural rough terrain covered by sands, gravel and rocks. This research focus the following three points :(1) Modeling of rover dynamics and tire mechanics that enable us to simulate the rover motion numerically,(2) Evaluation of the model by comparing the experimental observation and the numerical simulation,(3) Investigation of the navigation control laws for less slip, more efficient and safe operation.In the modeling of the rover dynamics, a simulation software toolbox named the SpaceDyn that works with MATLAB has been developed and applied. Mars exploration rovers under the development by NASA have a unique suspension system called Rocker-Bogie, which capability to go over obstacles was proven by Maars PathFinder mission in 1997. The Rocker-Bogie requires a complicated model of the force-torque equilibrium although, the SpaceDyn simulates such complicated motion of obstacle negotiation with relatively easy programming.In the experiments, key parameters to model the traction mechanics between the tire and soil are estimated. Slip and stack phenomena is observed with excessive loads and actuator torque saturation, when the rover is climbing up a slope for example. This phenomena is clearly simulated by the numerical model developed here with the experimentally identified traction coefficient versus slip.Based on the above observation and simulation analysis, it is suggested that (a) equal load distribution on all tires, or if the equalizing is difficult, (b) weighted tire torque distribution, shall be effective for the navigation control with higher efficiency and lower probability of slip, stack and tip-over.