Analytical and Experimental Investigation of Force Controlled Off-Road Wheeled Vehicles

本课题研究越野车轮式主动控制问题。有效控制这些系统中的力分布，特别是控制所有车轮-地形接触力，对于实现这些车辆的运动和悬挂自由度的可接受控制至关重要。在不平坦地形上，轮式车辆的运动学和准静力分布特性与在平坦地形上的车辆有着根本的不同。如果将车辆-地形组合作为一个具有封闭运动回路的空间连杆，则均匀的地形导致这些虚拟空间连杆具有固有的对称性。这种对称性导致了这些车辆的运动和静力分布行为的奇异性。关于传统车辆在均匀表面运行的文献并没有解决这些奇点，因为这些车辆在名义上是作为平面运动机器来研究的，它们的悬挂自由度很小。运动和悬浮通常被视为解耦问题。在不平坦的地形上，对称性和奇点并不总是存在。利用基于螺旋系统理论的运动学-几何框架，对轮式车辆在不平坦地形上的可动性（自由度数）和运动势（可用运动）进行了研究。该框架还可以通过将机器人经典问题中观察到的速率运动学/静力分析对偶性扩展到这类空间机构中来研究这些车辆的力分布特性。运动学几何框架特别适合研究主动越野车辆，因为它们的系统设计通常不包括有意的被动顺应（集中或分布）。对复杂系统刚体动力学的运动学几何方法的扩展，即空间矢量力学，用于研究这些越野车辆的动力学行为。该项目包括“分析/数值”和“实验”两个方面。分析/数值目标包括空间矢量力学（SVM）框架的发展，该框架结合了螺旋系统理论和使用空间矢量符号的牛顿-欧拉动力学。支持向量机框架允许以综合的方式进行调查；开发主动越野轮式车辆的通用运动学综合技术；开发模块化动态模拟器，对两类轮式车辆进行数值研究；并开发了主动越野车辆的系统级力控制策略。实验任务包括使用力控三轮车（FCT）的实验原型进行越野实验。FCT是一类主动车辆的代表，包括两轮轴，可以主动改变其轴长。

This research project deals with an active control of offroad wheeled vehicles. An effective control of the force distribution in these systems, particularly the control of all the wheel-terrain contact forces, is central to achieving acceptable control of the motion and suspension degrees of freedom of these vehicles. On uneven terrain, wheeled vehicles possess kinematic and quasi-static force distribution characteristics that are fundamentally different from those that vehicles possess on even terrain. If the vehicle-terrain combination are instantaneously treated as a spatial linkage with closed kinematic loops, an even terrain leads to an inherent symmetry in these virtual spatial linkeage. This symmetry leads to singularities in kinematic and static force distribution behavior of these vehicles. The literature on conventional vehicles for even surface operation does not address these singularities since these vehicles are nominally studied as planar motion machines with small perturbations in their suspension degrees of freedom. Motion and suspension are generally treated as decoupled problems. On uneven terrain, the symmetry and hence the singularities are not always present. Using a kinematic-geometric framework based on screw system theory, an understanding of the mobility (number of degrees of freedom) and the motion potential (available motion) of wheeled vehicles on uneven terrain is developed. This framework can also be used to study the force distribution characteristics of these vehicles by extending the rate kinematics/static force analysis duality that has been observed in classical problems in robotics to these kinds of spatial mechanisms. The kinematic-geometric framework is particularly suited for studying active off-road vehicles since their system designs typically do not include intentional passive compliances (lumped or distributed). An extension of the kinematic-geometric approach to rigid body dynamics of complex systems, known as spatial vector mechanics is used to study the dynamic behavior of these offroad vehicles. The project includes both the `analytical/numerical' and `experimental' aspects. The analytical/ numerical objectives include the development of a Spatial Vector Mechanics (SVM) framework that combines Screw System Theory and Newrton-Euler Dynamics using Spatial Vector Notation. The SVM framework allows the investigation in an integrated manner; to develop general kinematic synthesis techniques for active off-road wheeled vehicles; to develop a modular dynamic simulator for performing numerical studies of two classes of wheeled vehicles; and to develop system-level force control strategies for active off road vehicles. The experimental task include off-road experiments with an experimental prototype known as the Force controlled Tricycle (FCT). The FCT is representative of a class of active vehicles that include two-wheel axles that can actively vary their axle lengths.