CONTRIBUTION TO THE SCHEDULING OF TRAJECTORIES IN ROBOTICS

In this paper, we intend to propose a method for minimizing the cycle time of robotic tasks by using an optimal scheduling of trajectory poi nts: we consider functional points (welding or laser-cutting points on a car-body for example) that a rebut has to reach. The problem is to order these points in such a way that the global cycle time is minimum . Originally, this scheduling problem is similar to the well-known tra velling salesman problem. Among the algorithms used in combinatorial o ptimization, we have taken an interest in an original connectionist me thod called ''the elastic net method'', initially presented in an eucl idian two-dimension space, The method described in this article is ada pted for robotic purpose. It has been testee! in industrial cases and compared with a classical method in combinatorial optimization: the Li ttle's algorithm. The elastic net method is generalized to the specifi c case of robotics applications. The elastic net method is generalized in the case of non-redundant and redundant robots; we develop a simul taneous research of the optimal scheduling and of the optimal choice o f the configurations of the robot for each functional point. The optim al scheduling of the points of a trajectory in the case of redundant r obots is presented. We consider it to be the original contribution of this work. In the case of cluttered environments, the above algorithm is adapted by introducing a repulsion potential between the obstacles and the ''elastic''. This leads to the simultaneous research of the op timal scheduling and of the free path planning. The method, using a ne w kind of algorithm, leads to original and reliable results for minimi zing cycle time in robotics. (C) 1998 Elsevier Science Ltd. All rights reserved.