This paper presents a method for planning the motions of autonomous vehicles moving on general terrains. The method obtains the geometric path and vehicle speeds that minimize motion time consid- ering vehicle dynamics, terrain topography, obstacles, and surface mobility. The terrain is represented by a smooth cubic B patch, and the geometric path consists of a B spline curve mapped to the surface. The time optimal motions are computed by first obtaining the best ohstacle- free path from all paths represented by a uniform grid. This path is further optimized with a local optimization, using the optimal motion time along the path as the cost function and the control points of a B spline as the optimizing parameters. Examples are presented that demonstrate the method for a simple dynamic model of a vehicle moving on a mountainous terrain. I. INTRODUCTION T HE problem of motion planning of autonomous vehicles consistsof selecting the geometric path and vehicle speeds so as to avoi...

This paper addresses a problem of autonomous parking a nonholonomic (car-like) vehicle. This research work is carried out within the framework of the PRAXITELE project which aims to develop a future-oriented urban transportation system based on a fleet of electric computer-driven vehicles. At the present stage of the project, the designed vehicles have been equiped for the computer-driven motion and their autonomous abilities are being worked out. A practical approach to motion generation and control for autonomous parallel parking of a nonholonomic vehicle is proposed. It is based on range measurements to environmental objects around the vehicle. The motion generation and control is considered within the reactive control scheme to avoid collisions with obstacles. The developed approach is tested on a LIGIER electric autonomous vehicle and is illustrated by the experimental results obtained. 1. Introduction The autonomous parking problem attracts a great deal of attention from the re...

Abstract. Although routing is a well-studied problem in various contexts, there remain unsolved problems in routing edges for graph layouts. In contrast with techniques from other domains such as VLSI CAD and robotics, where physical constraints play a major role, aesthetics play the more important role in graph layout. For graphs, we seek paths that are easy to follow and add meaning to the layout. We describe a collection of aesthetic attributes applicable to drawing edges in graphs, and present a general approach for routing individual edges subject to these principles. We also give implementation details and survey di culties that arise in an implementation. 1

Practical aspects of motion generation and control for parking a nonholonomic autonomous vehicle are considered. An iterative algorithm for the parallel parking maneuver is proposed. It is based on ultrasonic range data processing. To control the steering angle and longitudinal velocity of the vehicle during the parking maneuver, sinusoidal reference functions are used. To prevent collisions, the maneuver is carried out as a reactive motion. The developed control is experimentally verified for a LIGIER electric autonomous vehicle. 1 Introduction This paper studies the autonomous parking of carlike (nonholonomic) vehicles. The objective of this task is to extend the autonomous abilities of electric vehicles being developed within the framework of the French PRAXITELE project. Motion generation and control for parking deals with computing reference functions for the steering and velocity servosystems of the vehicle. Traditionally, this is carried out on the basis of a reference path pro...

In this paper, we consider path planning for a car-like vehicle.

This paper presents our work on automatic parking of a smart car that relies on vision to estimate free parking slots. All problems involved in implementing an automatic parking behavior are discussed. Solutions are given together with experimental results obtained from real data.

This paper deals with path planning for car-like robot. Usual planners compute paths made of circular arcs tangentially connected by line segments, as these paths are locally optimal. The drawback of these paths is that their curvature profile is not continuous: to follow them precisely, a vehicle must stop and reorient its directing wheels at each curvature discontinuity (transition segment-- circle). To remove this limitation, a new path planning problem is proposed: two curvature constraints are added to the classical kinematic constraints taken into account. Thus, the curvature must remain continuous, and its derivative is bounded (as the car-like robot can reorient its directing wheels with a limited speed only). For this problem, the existence of solutions and the characterization of those of optimal length are shown. A method solving the forward-only problem (i.e. the problem for a car moving only forward) is then presented, and this method is compared to the classical one w.r.t...

Outdoor mobile robot motion planning and navigation is a challenging problem in artificial intelligence. The search space density and dimensionality, system dynamics and environmental interaction complexity, and the perceptual horizon limitation all contribute to the difficultly of this problem. It is hard to generate a motion plan between arbitrary boundary states that considers sophisticated vehicle dynamics and all feasible actions for nontrivial mobile robot systems. Accomplishing these goals in real time is even more challenging because of dynamic environments and updating perception information. This thesis develops effective search spaces for mobile robot trajectory generation, motion planning, and navigation in complex environments. Complex environments are defined as worlds where locally optimal motion plans are numerous and where the sensitivity of the cost function is highly dependent on state and motion model fidelity. Examples include domains where obstacles are prevalent, terrain shape is varied, and the consideration of terramechanical effects is important. Three specific contributions are accomplished. First, a model-predictive trajectory generation technique is developed that numerically linearizes and inverts general predictive motion models to determine parameterized actions that satisfy the two-point boundary value problem. Applications on a number of mobile robot platforms (including skidsteered field robots, planetary rovers with actively articulating chassis, mobile manipulators, and autonomous automobiles)

We study the problem of computing a planar curve, restricted to lie between two given polygonal chains, such that the integral of the square of arc-length derivative of curvature along the curve is minimized. We introduce the Minimum Variation B-spline problem which is a linearly constrained optimization problem over curves defined by Bspline functions only. An empirical investigation indicates that this problem has one unique solution among all uniform quartic B-spline functions. Furthermore, we prove that, for any B-spline function, the convexity properties of the problem are preserved subject to a scaling and translation of the knot sequence defining the B-spline. 1

: This paper presents a set of paths, called bi-elementary paths. These paths are smooth and feasible for a car-like robot (i.e. their tangent direction is continuous and they respect a minimum turning radius constraint), and they can be followed by a real vehicle without stopping (i.e. they have a continuous curvature profile) --- which is not the case of Dubins' curves. These paths are composed of arcs of clothoid (a clothoid is a curve whose curvature is a linear function of its arc length), and are used to define a simplified, i.e. non complete, planner. This simplified planner is, in turn, used in two global planning schemes, namely the Ariadne's Clew algorithm and the Probabilistic Path Planning. This paper proves an important property of the bi-elementary paths, from which the completeness of the two global planners is deduced. Keywords --- mobile-robot, path-planning, non-holonomic-system, continuous-curvature paths, clothoids, global planner, completeness. Acknowledgements ...