Journal of lntelligent and Robotic Systems 11: 223-267, 1995. © 1995 Kluwer Academic Publishers. Printed in the Netherlands. 223 Optimal and Suboptimal Motion Planning for Collision Avoidance of Mobile Robots in Non-stationary Environments K. J. KYRIAKOPOULOS New York State Centerfor Advanced Technology in Automation and Robotics and G. N. SARDIS NASA Center of Intelligent Robotic Systems for Space Exploration Rensselaer Polytechnic Institute, Troy, NY I2180-3590, U.S.A. (Received: 9 February 1993; in final form: 13 July 1993) Abstract. An optimal control formulation of the problem of collision avoidance of mobile robots moving in terrains containing moving obstacles is presented. A dynamic model of the mobile robot and the dynamic constraints are derived. Collision avoidance is guaranteed if the minimum distance between the robot and the objects is nonzero. A nominal trajectory is assumed to be known from off-line planning. The main idea is to change the velocity along the nominal trajectory so that collisions are avoided. Furthermore, time consistency with the nominal plan is desirable. Two solutions are obtained: (1) A numerical solution of the optimization problem and a perturbation type of control to update the optimal plan and (2) A computationally efficient method giving near optimal solutions. Simulation results verify the value of the proposed strategies and allow for comparisons. Key words. Mobile robots, motion planning, collision avoidance,, moving obstacles 1. Introduction The trend to install several autonomous machines within the same environment raises questions about their interaction with their human 'associates', and between themselves. Naturally, the issue of safety and efficient cooperation surfaces. Although a potential solution to this problem is priority assignment by a central control unit, this would contradict the obvious design specification regarding maximal 'autonomy'. Therefore, a solution where a central control unit assigns only simple tasks specified by qualitative requirements, leaving the lower level decision making to be performed within the conceptual (or physical) limits of an autonomous machine, is desirable. The problem of 'moving robot or a manipulator from an initial position of the workspace to a final one, avoiding the stationary obstacles of the environment