436 research outputs found
What is the use of the body schema for humanoid robots?
No full textThe paper explains the necessity, for humanoid robots, of the body schema, as a middleware between motor cognition and motor control. A specific model of body schema is described, based on the Passive Motion Paradigm, which uses force fields for representing goals and internal/external constraints. The integration of the body schema with motor control is discussed in relation with whole body movements. Finally, the integration with sensorimotor cognitive processes is addressed, in the context of learning/discovering the use of tools in skilled behavior. © 2013 World Scientific Publishing Company
Stabilization strategies for unstable dynamics.
No full textBACKGROUND: When humans are faced with an unstable task, two different stabilization mechanisms are possible: a high-stiffness strategy, based on the inherent elastic properties of muscles/tools/manipulated objects, or a low-stiffness strategy, based on an explicit positional feedback mechanism. Specific constraints related to the dynamics of the task and/or the neuromuscular system often force people to adopt one of these two strategies. METHODOLOGY/FINDINGS: This experiment was designed such that subjects could achieve stability using either strategy, with a marked difference in terms of effort and control requirements between the two strategies. The task was to balance a virtual mass in an unstable environment via two elastic linkages that connected the mass to each hand. The dynamics of the mass under the influence of the unstable force field and the forces applied through the linkages were simulated using a bimanual, planar robot. The two linkages were non-linear, with a stiffness that increased with the amount of stretch. The mass could be stabilized by stretching the linkages to achieve a stiffness that was greater than the instability coefficient of the unstable field (high-stiffness), or by balancing the mass with sequences of small force impulses (low-stiffness). The results showed that 62% of the subjects quickly adopted the high-stiffness strategy, with stiffness ellipses that were aligned along the direction of instability. The remaining subjects applied the low-stiffness strategy, with no clear preference for the orientation of the stiffness ellipse. CONCLUSIONS: The choice of a strategy was based on the bimanual coordination of the hands: high-stiffness subjects achieved stability quickly by separating the hands to stretch the linkages, while the low-stiffness subjects kept the hands close together and took longer to achieve stability but with lower effort. We suggest that the existence of multiple solutions leads to different types of skilled behavior in unstable environments
Self-Organizing Body Schema for Motor Planning
No full textThis article presents a distributed computational architecture for the motor planning functions of the posterior parietal cortex, which is organized as a computational map and combines a paradigm of self-organization (for building robust and coherent maps of the different motor spaces) with an attractor dynamics (for run-time integration of task constraints). The model, named SO-BoS (self-organizing body-schema), is illustrated with simple simulation results
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