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Planning robust grasping operations involving a dextrous robotics hand and an object located in a three dimensional workspace requires to combine two main types of techniques: a geometric reasoning technique aimed at producing a grasping strategy (preshape of the hand, grasping parameters, type of motion to execute), and a physically based technique, allowing the analysis of the dynamic object/hand interactions. This paper focus on the second type of technique which is clearly required to conclude on the feasibility of the chosen grasping strategy (stability in particular) and to determine the execution parameters of the selected grasp (type of control to apply onto the hand in particular .nique based upon the concept of "physical models" for solving this problem. We will show how physical models can be constructed and used t o solve the assocaated stability and control strategy problems. We will also show how the related techniques has been combined with more classical geometric methods to solve the whole problem.

ftp://ftp.inrialpes.fr/pub/sharp/publications/joukhadar:etal:iros:99.pdf.gz (not accepted here, non vectorial font)/http://www.ieee.orgThis paper presents an approach to detect and localize contact between deformable polyhedra, which can be convex or concave depending on the time step. Usual contact detection algorithms, defined for convex polyhedra, cannot be used efficiently as they would imply to compute the convex decomposition of the considered polyhedra at each time step, as it can change due to the deformability of these polyhedra. The computation of this convex decomposition being very expensive (in complexity and computation time), we propose an algorithm to detect and localize the contact in linear time wrt the number of vertices. This algorithm returns the direction of this contact and the value of the maximum intersection distance between the convex hulls of the two considered polyhedra. Experimental results, taken from a dynamic simulation application, are presented with their computation time to complete the complexity analysis

Although accurate predictions of the behavior and function of the anterior cruciate ligament would aid in diagnosis and operative treatment, no agreement exists on the best way to model the ligament with a reliable description of its mechanical and geometric features. We propose a new model of the anterior cruciate ligament based on multiple viscoelastic curvilinear fibers. This model was used for quasi-static simulations of the passive motion of eight porcine knees, after registration of the passive trajectories and digitization of the surface of the ligament in flexion. Simulations of anterior cruciate ligament deformations during passive motion predicted a fiber strain of less than 20%, low insertion forces, and isometric anterior fibers. The model explains actions of the ligament fibers, as reported in the literature, better than classic models based on linear fibers and consistent with the mechanical properties of the anterior cruciate ligament.