This paper addresses the problem of computing stable grasps of 2-D polygonal objects. We consider the case of a hand equipped with three hard fingers and assume point contact with friction. We prove new sufficient conditions for equilibrium and force closure that are linear in the unknown grasp parameters. This reduces computing the stable grasp regions in configuration space to constructing the three-dimensional projection of a five-dimensional polytope. We present an efficient projection algorithm based on linear programming and variable elimination among linear constraints. Maximal object segments where fingers can be positioned independently while ensuring force closure are found by linear optimization within the grasp regions. The approach has been implemented and several examples are presented.

This paper addresses motion planning for a mobile robot moving on a hilly three dimensional terrain and subjected to strong physical interaction constraints. The main contribution of this paper is a planning method which takes into account the dynamics of the robot, the robot/terrain interactions, the kinematic constraints of the robot, and classical constraints. The basic idea of our method is to integrate geometric and physical models of the robot and of the terrain in a two-stage trajectory planning process. Consisting in combining a "discrete search strategy" and a "continuous motion generation method". It will be shown how each planning step operates and how they interact in order to generate a safe and executable motion for the all-terrain vehicle.>

This paper deals with the problem of simulating the behavior of a mobile robot moving on a terrain along a precomputed nominal path. The nominal path is supposed to be provided by a planner. The purpose of the simulator to instantiate the nominal path into a complete trajectory, while verifying that a set of constraints is satisfied all along the motion. The simulator is based on an iterative algorithm to compute configurations for the robot at each time increment. Each iteration consists of two successive steps: determination of a stable configuration and of the associated contact points on the ground, and determination of the motion of all joints by minimization of the sliding at the contact points.

Thzs paper presents a system for plannzng and executzng stable grasps of curved two-damenszonal objects. We conszder the case of a hand equzpped wzth two hard fingers and assume poznt contact wzth frzctzon Objects are modelled by parametrzc curves, and force-closure grasps are characterzzed by systems of polynomzal constraints an the parameters of these curves. All configuratzon space regzons satzsfyzng these constraznfs are found by a parallel numerzcal cell decomposztzon algoriihni based on curve tracing and continadzon techniques ~IULLIILU~ object segiiienls diel e fingers can be positzoned an depeii dently are found by optimzzateon wzlhzn the grasp regaons The approuch has been implemented uszng a dzstrzbuted archztecture, and experzinents using a PUMA rohot equipped ubiih a pneumatzc two-finger grippe? aid U vzszoii system are presented

An approach to the computation of stable grasps of curved two-dimensional objects is presented. The authors consider the case of a hand equipped with two hard fingers and assume point contact with friction. Objects are modeled by parametric curves, and force-closure grasps are characterized by systems of polynomial constraints in the parameters of these curves. All configuration space regions satisfying these constraints are found by a numerical cell decomposition algorithm based on curve tracing and continuation techniques. Maximal object segments where fingers can be positioned independently are found by optimization within the grasp regions. The approach has been implemented and examples are presented.>

The authors describe ACT, a system designed to plan and monitor robot motions using a geometric representation of the environment. The goal in developing ACT was to design a system which could be used in industrial applications as well as a software basis to develop new robot programming techniques in the academic environment. ACT is intended to provide the user with advanced programming tools such as inline path planning and graphic monitoring of robot tasks. The project included developments not directly related to robotics but which were essential to enhance these new programming techniques. For example, a special user interface was developed to specify the robot tasks as well as to interface with existing CAD modelers. The authors present the technical choices made in developing the system and the most technically innovative parts of the system.>

The author presents an offline programming system specially designed for complex robotic applications (e.g., intervention of redundant manipulators in a nuclear plant). It uses hierarchical CAD models of solids and manipulators. These models are derived from constructive solid geometry trees and combine simple volume primitives with union or difference set operations. They offer different levels of description of the objects and enable an efficient computation of local minima of the distance between points of the objects. By setting constraints on the variation of the distance at these points, it is possible to produce collision-free trajectories achieving complex tasks with Cartesian and/or joint parameter goals.>

A general and simple algorithm is presented which computes the set FP of all free configurations for a polygonal object I (with m edges) which is free to translate and/or to rotate but not to intersect another polygonal object E. The worst-case time complexity of the algorithm is O(m/sup 3/n/sup 3/ log mn), which is close to optimal. FP is a three-dimensional curved object which can be used to find free motions within the same time bounds. Two types of motion have been studied in some detail. Motion in contact, where I remains in contact with E, is performed by moving along the faces of the boundary of FP. By partitioning FP into prisms, it is possible to compute motions when I never makes contact with E. In this case, the theoretical complexity does not exceed O(m/sup 6/n/sup 6/ alpha (mn)) but it is expected to be much smaller in practice. In both cases, pseudo-optimal motions can be obtained with a complexity increased by a factor log mn.>

This paper presents an alternative to the Potential Field Method of computing local collision-free motions for general manipulators. The main distinction is that we separate the description of the task from constraints of anti-collision. This enables to control accurately all relevant measures of the problem. A task is expressed by the minimization of a function plus eventually some geometric constraints, whereas anti-collision is translated into very simple linear constraints through the methods of the velocity dampers and the tangent separating planes. This approach is applied to the control of manipulators with a high number of degrees of freedom, using hierarchical descriptions of the environment and the robots. This is illustrated by two realizations, path planning for a ten link manipulator in the cluttered environment of a nuclear plant reactor, and cooperative tasks between two six degree of freedom robots. In the end we discuss how to incorporate the action of a global planner in this general framework.

This paper deals with the problem of coping with noise disturbing data in Stereo, 3-D modelling and navigation. We introduce the idea of a Realistic Uncertain Description of the Environment (RUDE) which is local, i.e attached to a specific reference frame, and incorporates both, information about the geometry and about the parameters measuring this geometry. We also relate this uncertainty to the pixel uncertainty and show how the RUDE corresponding to different frames can be used to relate these frames by a rigid displacement which we describe both by a rotation and translation and a measure of their uncertainty. Finally, we use the relations between frames to update the associated RUDE and decrease their uncertainty.

We present a system designed for object level programming of industrial robots. It contains essentially four modules : - a C.A.D. module to build geometric models of objects and manipulators and define the implantation of the robotic cell. - a pre-processing module which uses the cell model to compute a representation of the free-space in the joint space of the robot arm. - an obstacle avoidance module which uses this representation to perform different tasks such as testing or searching a safe trajectory. - a planning module that combines the elementary tasks of the obstacle avoidance module to get the environment from its current state to the state defined by an object level instruction. It can be used either during the conception step of a robotic cell or for programming fastly and safely an industrial robot.

An automatic system for planning safe trajectories for a computer controlled manipulator among obstacles is a key component of robot assembly operations. This paper describes an algorithm transforming cartesian obstacles into obstacles in the space of the first three joints of a manipulator with six revolute joints (e.g. a ACMA-CRIBIER V80), and giving a hierarchical description of the free space by mean of an octree. Such a description is very useful in testing for collision between the arm of the manipulator end obstacles since it is represented by a point in this space.