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

本课题研究的是越野轮式车辆的主动控制问题。有效地控制这些系统中的力分布，特别是控制所有车轮与地面的接触力，是实现对这些车辆的运动和悬挂自由度的可接受控制的核心。在不平坦的地形上，轮式车辆具有与平坦地形上的车辆根本不同的运动和准静态的力分布特性。如果瞬时将车辆-地形组合视为具有闭合运动学回路的空间连杆，则平坦的地形导致这些虚拟空间连杆中固有的对称性。这种对称性导致了这些车辆的运动力和静态力分布行为的奇异性。关于均匀表面操作的传统车辆的文献没有解决这些奇点，因为这些车辆名义上被研究为具有悬架自由度小扰动的平面运动机器。运动和悬架通常被视为解耦问题。在不平坦的地形上，对称性并不总是存在，因此奇点也不总是存在。利用基于螺旋系统理论的运动学几何框架，发展了对轮式车辆在不平坦地形上的机动性(自由度)和运动势(可用运动)的理解。通过将机器人经典问题中观察到的速率运动学/静力分析对偶推广到这类空间机构，该框架还可以用于研究这些车辆的力分布特性。运动学-几何框架特别适合于研究主动越野车辆，因为它们的系统设计通常不包括故意的被动遵从(集中或分布式)。将运动学-几何学方法扩展到复杂系统的刚体动力学，称为空间矢量力学，用于研究这些越野车辆的动力学行为。该项目包括“分析/数字”和“实验”两个方面。分析/数值目标包括开发空间向量力学(SVM)框架，该框架结合了螺旋系统理论和使用空间向量符号的牛顿-欧拉动力学。支持向量机框架允许以一种综合的方式进行研究；开发用于主动越野轮式车辆的通用运动学综合技术；开发用于对两类轮式车辆进行数值研究的模块化动态模拟器；以及开发用于主动越野车辆的系统级力控制策略。实验任务包括用一种名为力控制三轮车(FCT)的实验原型进行越野实验。FCT是一类主动车辆的代表，它包括两个轮轴，可以主动改变轴长。

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.