Journal of Intelligent and Robotic Systems 24: 347–366, 1999. © 1999 Kluwer Academic Publishers. Printed in the Netherlands. 347 A Shortest Path Based Path Planning Algorithm for Nonholonomic Mobile Robots KAICHUN JIANG ⋆ Manufacturing Engineering and Industrial Management, Department of Engineering, The University of Liverpool, Liverpool L69 3BX, UK; e-mail: kaichun@liverpool.ac.uk LAKMAL D. SENEVIRATNE and S. W. E. EARLES Department of Mechanical Engineering, King’s College London, Strand, London WC2R 2LS, UK (Received: 25 May 1998; accepted: 5 October 1998) Abstract. A path planning algorithm for a mobile robot subject to nonholonomic constraints is pre- sented. The algorithm employs a global-local strategy, and solves the problem in the 2D workspace of the robot, without generating the complex configuration space. Firstly, a visibility graph is con- structed for finding a collision-free shortest path for a point. Secondly, the path for a point is evaluated to find whether it can be used as a reference to build up a feasible path for the mobile robot. If not, this path is discarded and the next shortest path is selected and evaluated until a right reference path is found. Thirdly, robot configurations are placed along the selected path in the way that the robot can move from one configuration to the next avoiding obstacles. Lemmas are introduced to ensure that the robot travels using direct, indirect or reversal manoeuvres. The algorithm is computationally efficient and runs in time O(nk + n log n) for k obstacles and n vertices. The path found is near optimal in terms of distance travelled. The algorithm is tested in computer simulations and test results are presented to demonstrate its versatility in complex environments. Key words: motion planning, nonholonomic robot, constraints, visibility graph, reversal manoeu- vres. 1. Introduction A nonholonomic mobile robot usually has typical features of a car, such as a rec- tangular shaped body and a limited steering angle. Although vehicles with those features are used in numerous applications, research results in general motion plan- ning for nonholonomic robots are hardly adopted into autonomous vehicles. Two facts have contributed to the complication of the problem. One is the rectangular shape of the robot. This shape rules out the possibility of using some algorithms which requires the robot to be circular, or triangular. The other fact is that the non- holonomic constraints on a mobile robot give strict requirement on the curvature of the path, which general path planners cannot satisfy. ⋆ Corresponding author. VTEX(P) PIPS No.: 193930 (jintkap:mathfam) v.1.15