A computerized dynamic synthesis method for generating human aerial movements

A computerized method based on optimal dynamic synthesis was developed for generating the flight phase of somersaults. A virtual gymnast is modeled as a planar seven-segment multibody system with six internal degrees of freedom. The aerial movement is generated using a parametric optimization technique. The performance criterion to be minimized is the integral quadratic norm of the torque generators. The method produces realistic movements showing that somersaults perfectly piked or tucked appear spontaneously according to the value of the rotation potential of the initial movement. It provides accurate knowledge of the evolution of joint actuating torques controlling the somersault, and makes it possible to investigate precisely the configurational changes induced by modifications of the rotation potential. Four simulations are presented: one with a reference value for the rotation potential, two with reduced values, and the last with a different hip flexion limit. They give an insight into the coordination strategies which make the movement feasible when the rotation potential is decreased. The method gives accurate assessments of the energetic performance required, together with precise evaluations of the mechanical efforts to be produced for generating the acrobatic movement

Control of a Biped Robot by Total Rate of Angular Momentum Using the Task Function Approach

In this work we address the control problem of biped robots by using the task function approach. A problem arrives when one of the feet is in contact with the ground, which presents imperfections. There is then the possibility that the biped robot undergoes a fall. It is difficult to track any trajectory due to the presence of unevenness on the ground. What we propose is to use the task function approach combined with the application of the total rate of angular momentum to obtain a control law for the ankle. By this technique, the tracking becomes more smooth and the balance is assured. The control law proposed allows the upper part of the robot to be controlled independently since only the ankle actuators are concerned. We enounce the formal problem and present some simulations with real parameters of a 21 degrees of freedom biped robot

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Walking pattern synthesis is carried out using a spline-based parametric optimization technique. Generalized coordinates are approximated by spline functions of class C 3 fitted at knots uniformly distributed along the motion time. This high-order differentiability eliminates jerky variations of actuating torques. Through connecting conditions, spline polynomial coefficients are determined as a linear function of the joint coordinates at knots. These values are then dealt with as optimization parameters. An optimal control problem is formulated on the basis of a performance criterion to be minimized, representing an integral quadratic amount of driving torques. Using the above spline approximations, this primary problem is recast into a constrained non-linear optimization problem of mathematical programming, which is solved using a computing code implementing an SQP algorithm. As numerical simulations, complete gait cycles ar

Energetic versus sthenic optimality criteria for gymnastic movement synthesis

Dynamic synthesis of human movements raises the question of the selection of a suitable performance criterion able to generate proper dynamic behaviors. Two quite different criteria are likely to be appropriate candidates: the minimum effort cost (or sthenic criterion) and the minimum energy cost. The paper is aimed at clarifying the dynamic effects of these two fundamental criteria when considering movements executed with liveliness as they are in gymnastic. It is well known that the former cost generates movements with smooth dynamics. A special attention is devoted to the latter. The optimal control theory shows that minimizing the energy consumption results in actuating inputs of bang-off-bang type producing momentum impulses. When achieving dynamic synthesis, this criterion makes necessary to account for bounds set on driving torques. Moreover, when dealing with onesided contacts, as in floor handstands, the unilaterality of contact forces must be explicitly accounted for since it tends to be infringed by impulsive efforts. Numerical simulations of these formal properties are carried out using a parametric optimization technique, and considering the raising phase of floor handstands. It is shown that the energetic criterion tends to generate movements which exhibit similarities with their real counterpart performed by an expert gymnast. Conversely, the sthenic criterion produces movements quite different. But, a salient fact is that these ones proved to be easier to perform by young beginners. As a result, they could help to coach novice gymnasts

Détermination des efforts articulaires exercés au cours de trois types d'élan en barre fixe

Contraintes mécaniques articulaires engendrées par l'optimisation de l'élan circulaire préparatoire à la réalisation de la figure acrobatique 'tkatchev' à la barre fixe. La réussite de cette acrobatie nécessite de produire, à la hanche et à l'épaule, des moments importants pour réaliser des actions de fouettés du corps de 125° à 160°