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. 2014 Jan 16;7:191. doi: 10.3389/fncom.2013.00191

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Copyright © 2014 Alessandro, Carbajal and d'Avella.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Results of reversal tasks. (A) Selection of proto-tasks based on projection error. Each panel shows the kinematic chain in its initial posture (straight segments), and the distribution of the projection error over the end-effector space (colored region). The color of each point indicates the projection error produced to reach that position and to go back to the initial posture. The bottom right panel shows the distribution of the forward dynamics error of the end-effector using eight proto-tasks (eight synergies). (B) Averaged projection error as a function of the number of proto-tasks for increasingly general classes of via-point tasks. The least general tasks are reversal motions (blue continuous line), characterized by two free task-parameters (i.e., configuration of the intermediate target). An increase in generality consists in fixing only the initial posture, while intermediate target and final position represents free task-parameters (red dotted line). Finally the most general class (green dashed line) does not fix any posture (six free task-parameters). The number of synergies required to achieve the same error increases with the generality of the class of tasks. These results are discussed in section 3.4. (C) Evaluation of the reduction phase for the testing reversal tasks. Comparison between the synthesized synergies (filled circles) and subsets randomly selected from the exploration-actuations (box-plots). (D) Actuation that solves the task (continuous lines) and projected (dashed lines) torque, and interpolated (continuous lines) and executed (dashed lines) joint trajectories for the tasks with the highest projection error (i.e., target 11).