Regresar

Trajectory Planner for Type II Singularities Avoidance Based on Output Twist Screws

Abstract:

Motion planning of manipulators is a major discipline in robotics that involves the generation of feasible trajectories within the workspace so that neither collisions nor singularities are encountered during its execution. The singularity issue is of paramount importance in parallel robots (PRs) which, despite their capability of performing very accurate movements, suffer from the so-called Type II singularities. These singular configurations occur within the workspace, and a PR loses control when approaching such configurations. In this paper, an algorithm for Type II singularities avoidance in PRs is proposed that allows to i) create a new trajectory from an initial to a final configuration that is non-singular, and ii) adapt an existing trajectory that goes through singular configurations so that the new generated trajectory evades them with minimum modifications of the original path. The new trajectory may serve as a reference position for safe control of a PR, and it is used in an experiment on a real 4-DOF PR meant for knee rehabilitation, with a position controller to follow the trajectory. The results show how the initially unstable behavior when following an original singular trajectory can be fixed after modifying that trajectory with the proposed algorithm.