Jean-Rémy CHARDONNET, Ph.D.

Ph.D. thesis (2006-2009)

The topics of my Ph.D. thesis, from Montpellier II university, was interactive dynamic simulation for virtual avatars, applied to humanoid robots. Simulators is of primary concern in the development of humanoids because they allow the validation of theoritical models on expensive systems. Robots are aimed at evolving in environments involving complex phenomena. A good simulator must hence address these issues in a realistic and robust way. This thesis was done in the frame of the IMMERSENCE European project, at the Joint Robotics Laboratory (JRL), Tsukuba, Japan, and at the LIRMM lab, Montpellier, France.

The JRL lab already used a dynamic simulator for humanoid robots, OpenHRP. However it used penalty-based contact resolution methods, giving unstable simulations, especially for object grasping simulations, and was not interactive. Therefore the goal was to propose an interactive simulator with a modular architecture, that solves contact problems in a robust, realistic and real-time way.

Implemented models in the developed simulator. To solve contact problems, constrained-based methods are used. These methods explicitely include non-penetration constraints in the dynamics equations, allowing to get a linear relation between the acceleration of contact points and contact forces. Coupled to constraints, this problem becomes a Linear Complementarity Problem (LCP). Adding Coulomb's friction complexifies the problem because the friction law is non-linear. Consequently, the LCP formulation cannot be kept, unless Coulomb's law is discretized. However, discretization implies an increase of computation time with a decrease of accuracy. Iterative methods do not need any discretization and allow to keep a compromise between speed and accuracy. The complexity of the global algorithm is quadratic in the number of contact points. To improve simulation speed, a new algorithm to compute the contact space inertia matrix, also called the Delassus operator, used in the resolution of contact forces and usually time consuming, was written.

Basic simulations. The model used for the simulations is the HRP-2 humanoid robot. Different scenarii involving complex environments and manipulation tasks were tested. The dynamic simulator is part of a modular framework called AMELIF and aimed at virtual prototyping. This simulator has also been used to write the next version of OpenHRP, OpenHRP3.

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Interactivity. The high modularity of the framework allowed to quickly integrate the possibility for a user to interact in real time with the elements of the virtual scene, for example to achieve collaborative tasks. A haptic device with force feedback, here an OMNI, was interfaced with the simulator to allow mainly two kinds of interaction: touching and grasping.

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Extensions.

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Validation of the simulator. Experiences were conducted on the HRP-2 robot to validate the models implemented in the simulator. Several parameters, such as the friction coefficients between the robot and the environment, actuators' parameters and force sensors' parameters, were measured. The validation was performed on a simple example.

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Applications. The simulator has been used for real applications of humanoid robotics, more specifically for grasping large and heavy objects in a dynamic way. This application, which is extreme, allows to see whether the models implemented in the simulator are relevant and, more generally, is a strong way to assess the simulator.

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Scientific publications

Other publications