A switching inverse dynamics controller for parallel manipulators around drive singular configurations

Abstract

Despite many advantages, parallel manipulators are known to possess drive singularities where the control of one or more degrees of freedom is lost. Around these singular configurations, the required actuator forces grow unbounded. Previous efforts in the literature put forward singularity-consistent trajectory planning and singularityrobust modification of the dynamic equations as a solution to this problem. However, this previous method is applicable only for the open-loop operation of the manipulator, whereas initial configuration errors, external disturbances, and modeling errors should necessarily be taken into account in a closed-loop sense in real-life applications. With this aim, a switching inverse dynamics controller is proposed in this study for the trajectory tracking control of parallel manipulators as they pass through drive singular configurations. Simulations of the application of the developed controller result in good tracking performance, even in the presence of modeling errors, while the actuator efforts remain bounded and continuous in the neighborhood of the singularity.

Certified detection of parallel robot assembly mode under Type 2 singularity crossing trajectories

“…It emerged with the discovery of a physical criterion allowing the non-degeneracy of the manipulator's dynamic model in Type 2 singular configurations [11]. Using this criterion, trajectory planners and dedicated multi-model Computed Torque Control schemes [13] [14] have been developed and tested, proving their efficiency in most cases. Nevertheless, unavoidable tracking errors with respect to this desired trajectory can have a strong impact in the vicinity of the singularity, up to missing the assembly mode change.…”