A three-dimensional, self-reconfigurable structure is proposed. The structure is a fully distributed system composed of many identical 3-D units. Each unit has functions of changing local connection, information processing, and communication among neighborhood units. Groups of units cooperate to change their connection so that the shape of the whole solid structure transforms into arbitrary shape. Also, the structure can repair itself by rejecting faulty units, replacing them with spare units. This kind of self-maintainability is essential to structure's longevity in hazardous or remote environments such as space or deep sea, where human operators cannot approach. We have designed and built a prototype unit to examine the feasibility of the 3-D self-reconfigurable concept. The design of the unit, method of reconfiguration, hardware implementation, and results of preliminary experiments are shown. In the last part of this paper, distributed software for self-reconfiguration is discussed.
Abstract-Our work builds largely on Nagasaka's stabilizer in multi-contact motion [1]. Using a sequence of contact stances from an offline multi-contact planner, we use first a Model Predictive Controller to generate a dynamic trajectory of the center of mass, then a whole-body closed-loop model-based controller to track it at best. Relatively to Nagasaka's work, we allow frame changes of the preferred force, provide a heuristic to compute the timing of the transition from purely geometrical features and investigate the synchronization problem between the reduced-model preview control and the whole-body controller. Using our framework, we generate a wide range of 3D motions, while accounting for predictable external forces, which includes transporting objects. Simulation scenarios are presented and obtained results are analyzed and discussed.
We propose a method to plan optimal whole-body dynamic motion in multi-contact non-gaited transitions. Using a B-spline time parameterization for the active joints, we turn the motion-planning problem into a semi-infinite programming formulation that is solved by nonlinear optimization techniques. Our main contribution lies in producing constraint-satisfaction guaranteed motions for any time grid. Indeed, we use Taylor series expansion to approximate the dynamic and kinematic models over fixed successive time intervals, and transform the problem (constraints and cost functions) into time polynomials which coefficients are function of the optimization variables. The evaluation of the constraints turns then into computation of extrema (over each time interval) that are given to the solver. We also account for collisions and self-collisions constraints that have not a closed-form expression over the time. We address the problem of the balance within the optimization problem and demonstrate that generating whole-body multi-contact dynamic motion for complex tasks is possible and can be tractable, although still time consuming. We discuss thoroughly the planning of a sitting motion with the HRP-2 humanoid robot and assess our method with several other complex scenarios.
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