Abstract. Teaching simulated creatures how to walk and run is a challenging problem. As with a baby learning to walk, however, the task of synthesizing the necessary muscle control is simplified if an external hand to assist in maintaining balance is provided. A method of using guiding forces to allow progressive learning of control actions for balanced locomotion is presented. The process has three stages. Stage one involves using a "hand of God" to facilitate balance while the basic actions of a desired motion are learned. Stage two reduces the dependence on external guidance, yielding a more balanced motion. Where possible, a third stage removes the external guidance completely to produce a free, balanced motion. The method is applied to obtain walking motions for a simple biped and a bird-like mechanical creature, as well as walking, running, and skipping motions for a human model of realistic proportions.

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This paper describes a method that facilitates the use of physically based models by animators. The main point is to give the animator a familiar interface, while providing a simulation module which detects collisions thus enhancing realism. The user gives a set of key-frames to guide motion, but does not have to address problems such as interpenetration avoidance, deformations due to collisions, or realism of motion. The simulator will correct the trajectories and compute deformations according to each object's physical properties (such as mass, inertia, stiffness) as well as the collisions and contacts automatically detected during motion. To achieve this, objects are provided with actuators capable of generating forces and torques computed via generalized Proportional-Derivative controllers. When deflected by external actions, actuated objects try to return to their initial path. Speed variations over time are computed during the simulation, and depend on the complexity of the paths, on the objects' models, and on the events such as collisions occurring during motion. In addition simulations are generated at interactive rates, even in the case of complex articulated objects. This facilitates the fine tuning of an animation sequence.

This paper presents a novel approach for facilitating the use of physically based models by animators. The idea is to let the user guide motion at a high level of control by giving approximate desired trajectories and synchronization constraints between the objects over time, while a simulation module computes the final motion, dealing with collision detection and response, and enhancing realism. The objects, which are either isolated or components of an articulated structure, are guided through the specification of key-position and orientations, defined in a referential that can be fixed or relative to another object. The animation sequence is scripted by specifying a graph of synchronization constraints between objects over time. During the animation, objects automatically regulate their speed in order to meet these constraints. Résumé Cet article présente une nouvelle approche pour faciliter l'utilisation de modèles physiques par les graphistes. L'idée est de laisser l'utilisateur guider l'animationà un haut niveau de contrôle en donnant une approximation des trajectoires désirées et des contraintes de synchronisation temporelles entre les objets. Un module de simulation calcule ensuite le mouvement final, gérant les détections et réponses aux collisions, tout en améliorant le réalisme. Les objets, isolés ou composants d'une structure articulée, sont guidés par la spécification de positions et orientations-clés, définies dans un repère fixe ou relatif a un autre objet. La séquence d'animation est définie par la spécification d'un graphe de contraintes de synchronisation entre les objets au cours du temps. Pendant l'animation, les objets régulent automatiquement leur vitesse pour satisfaire ces contraintes.