Journal of Intelligent and Robotic Systems 13: 263-278, 1995. 263 © 1995 Kluwer Academic Publishers. Printed in the Netherlands. Reduction of Free-space-loss for Good and Rapid 3D Path Planning of 6DOF Robots C. BALAGUER*, A. BARRIENTOS, F.J. RODRIGUEZ, R. ARACIL, E. A. PUENTE Divisidn de Ingenier{a de Sistemas y Automdtica (DISAM), Polytechnical University of Madrid, c/Jose Gutidrrez Abascal, 2, Madrid 28006, Spain and U. PETER Institut fiir Regelungstechnik, Technical University of Braunschweig Hans-Sommer-Strafle, 66, Braunschweig 3300, Germany (Received: 30 March 1993; in final form: 26 November 1993) Abstract. This paper deals with a new approach to solve the up to 6DOF robots global collision-free path planning. This problem seems to be more difficult when big or very long pieces are manipulated in cluttered and occupied environments. Moreover, the computational effort increases if the necessary path resolution is very high. The developed algorithm is based on the c-space technique. Different robot models are used for rapid c-spaces computation. Each one for different parts of a typical pick and place task. The algorithm selectively uses these global or local c-spaces. This strategy leads to fast global c-space computation without a considerable loss of free-space caused by the simplified robot model, and to quasi real-time local c-space computation. The paths searching in the computed c-spaces can be performed by several techniques: cell (cube) mapping, octree, and slice, which are rule-base selected in an adequate way. Finally, the results of the algorithm implementation in several real robots are presented. Key words. Path planning, collision detection, robot modelling, graph searching. 1. Introduction Task-level robot programming is one of the most important objectives in modem robot research. The aim of this level of programming is to develop a method to program the robot with simple commands instead of a unique programming language for each robot. In order to achieve this purpose, it is necessary to develop the ability to plan robots collision-free motions in complex environments. In the last few years, different methods have been developed in order to rep- resent the free-space. The potential field method, as used in a lot of algorithms (Amaris, 1991), is very time-consuming and presents serious problem because of * Now with University Carlos III of Madrid, c/Butarque, 15, 28911 Leganes (Madrid), Spain.