Patrick Chedmail

Robot mechanism synthesis and genetic algorithms

We propose to explore the problem of mechanism synthesis with an approach using genetic algorithms. We intend to study the case where there exist geometric constraints (as avoiding obstacles). More precisely, we are interested in the choice of robots (morphology and position) which has to follow a given trajectory among obstacles.

Design and positioning of a robot in an environment with obstacles using optimal research

The authors describe a general method of designing and positioning a robot in an environment in order to solve geometrical problems related to the accessibility of given zones. The approach is characterized by the use of two different types of representation of the solids and of the spaces: a CSG (constructive solid geometry) and an octree representation. Each is well adapted to solve two different problems: collision detection and description of the attained space. In addition, an automatic algorithm is used to design any robot related to any set of Denavit-Hartenberg parameters. The use of an optimal approach makes it possible to define the parameters of the robot and its position and orientation in the environment that satisfy the specified task.<<ETX>>

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.

A global analysis of following trajectories by redundant manipulators in the presence of obstacles

A global solution is given for the following problem: Given a continuous trajectory defined in a robotic site containing obstacles, and given a redundant manipulator in the site, is the manipulators end-effector able to track the trajectory? If yes, find all possible solutions (i.e., all feasible motions of the robots structure producing a continuous displacement of the end-effector along the trajectory) in order to further optimize the task. If not, find the feasible parts of the trajectory. Instead of considering the pre-image of the trajectory in the robots jointspace (which would involve handling n-dimensional spaces, where n is the number of degrees-of-freedom of the manipulator), the problem is stated in a (r+1)-dimensional space, where r is the degree of redundancy of the manipulator. Application examples are shown using 3-R planar manipulators.<<ETX>>