A distributed approach for access and visibility task with a manikin and a robot in a virtual reality environment

This paper presents a new method, based on a multi-agent system and on a digital mock-up technology, to assess an efficient path planner for a manikin or a robot for an access and visibility task taking into account ergonomic constraints or joint and mechanical limits. In order to solve this problem, the human operator is integrated in the process optimization to contribute to a global perception of the environment. This operator cooperates, in real time, with several automatic local elementary agents. The result of this work validates solutions through the digital mock-up; it can be applied to simulate maintainability and mountability tasks.     

On the connectivity of manipulator free workspace

This article presents a new topological characterization of the free workspace of manipulators moving among obstacles. The free workspace is the set of positions and orientations that the end-effector of the manipulator can reach, according to the joint limits of each of its links, and taking into account the obstacles of the environment. A classification of new connectivity properties of the free workspace is proposed, corresponding to different types of motions (point-to-point motions, following of continuous trajectories) that the manipulator can perform in the Cartesian space. For each property, a necessary and sufficient condition is given, which permits verification of the connectivity of the whole free workspace and leads to all the connected subspaces in it. These properties have been implemented in a Robotics C.A.D. system using octree representation of spaces. Some applications are presented, which show that this work is of primary interest for preparing off-line tasks, and is a new contribution to the problem of robotic cell layout design.     

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 points: we consider functional points (welding or laser-cutting points on a car-body for example) that a robot 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 travelling salesman problem. Among the algorithms used in combinatorial optimization, we have taken an interest in an original connectionist method called “the elastic net method”, initially presented in an euclidian two-dimension space. The method described in this article is adapted for robotic purpose. It has been tested in industrial cases and compared with a classical method in combinatorial optimization: the Little’s algorithm. The elastic net method is generalized to the specific case of robotics applications. The elastic net method is generalized in the case of non-redundant and redundant robots; we develop a simultaneous research of the optimal scheduling and of the optimal choice of the configurations of the robot for each functional point. The optimal scheduling of the points of a trajectory in the case of redundant robots 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 optimal scheduling and of the free path planning. The method, using a new kind of algorithm, leads to original and reliable results for minimizing cycle time in robotics.