Parallel manipulators are uncontrollable at force singularities due to the infeasibly high actuator forces required. Existing remedies include the application of actuation redundancy and motion planning for singularity avoidance. While actuation redundancy increases cost and design complexity, singularity avoidance reduces the effective workspace of a parallel manipulator. This article presents a path tracking type of approach to operate parallel manipulators when passing through force singularities. We study motion feasibility in the neighborhood of singularity and conclude that a parallel manipulator may track a path through singular poses if its velocity and acceleration are properly constrained. Techniques for path verification and tracking are presented, and an inverse dynamics algorithm that takes actuator bounds into account is examined. Simulation results for a planar parallel manipulator are given to demonstrate the details of this approach.

AbsIract-Even though parallel manipulators are nncontmllahle at force singular positions, our analysis reveals that motion through force singularities may be possible using a path tracking type of approach. This article establishes the condition for trackability of paths in the presence of force singularities, and presents the tools required to verify path trackability. Simulation results of a 2 DOF planar parallel manipulator are shown.

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