Hierarchical Constraint-Based Singularity Avoidance for Multi-Axis Robots

A generalized reflexive approach for Hierarchical Constraint-Based Singularity Avoidance (HCB-SA) is proposed and demonstrated for the multi-axis robot control of a six Degrees Of Freedom (DOF) hybrid manipulator system. The concept utilizes a dynamic adaptation of virtual constraints by introducing virtual damped actuation on the velocity control level and an anisotropic reflexive trajectory deflection depending on the robot constraints on the position control level. Redundant or low priority DOFs can be used to minimize the pose error in the more important DOFs reflexively without calculating new trajectories. Accordingly, the end-effector can be safely controlled in the vicinity of singularities and all constraints in the task and joint space can be surely hold. Furthermore, the proposed cascaded feedback control with the generalized HCB-SA algorithm is able to react on the presence of external disturbances which is validated using software-in-the-loop simulation on the real-time control system. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)