DYNAMICS AND NAVIGATION CONTROL OF PLANETARY EXPLORATION ROVERS

本研究的目的是研究行星探测车的运动动力学和导航控制方法，通过自然粗糙的地形覆盖的沙子，砾石和岩石。本文的研究工作主要集中在以下三个方面：（1）建立了探测车动力学模型和轮胎力学模型，并对探测车的运动进行了数值模拟;（2）通过实验观测和数值模拟的对比，对模型进行了评价;（3）研究了探测车的导航控制规律，以减少滑移，提高探测车的运行效率和安全性。美国宇航局正在研制的火星探测车有一个独特的悬挂系统，称为摇杆转向架，它的能力，通过障碍物证明了马尔斯路径使命在1997年。摇杆转向架需要一个复杂的力-力矩平衡模型，而SpaceDyn模拟这种复杂的越障运动相对容易编程。在实验中，对轮胎与土壤之间的牵引力学模型的关键参数进行了估计。滑动和堆栈现象观察到过度的负载和致动器扭矩饱和，当漫游车是爬上一个斜坡，例如。基于上述观察和模拟分析，建议（a）在所有轮胎上均匀分布载荷，或者如果均衡很困难，（B）加权轮胎扭矩分布，对于导航控制有效，具有更高的效率和更低的打滑概率，堆叠和翻倒。

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.