Singularity Avoidance for 6-DOF Robots Using Holonomic Base Through Task-Priority Approach

This paper investigates singularity avoidance strategies for six-degree-of-freedom (6-DOF) robots in mobile holonomic manipulation tasks, focusing on shoulder singularities. The study leverages the redundancy of the manipulator-base combination to dynamically manage external and virtual forces, ensuring smooth end-effector trajectories and enhanced system manipulability. A Task Priority (TP) framework is employed, where primary tasks focus on trajectory control, while secondary tasks handle singularity avoidance using null-space projections and admittance controllers. Experimental results validate the approach, demonstrating that for repetitive tasks, upon the first encounter with a singularity, the robot is able to minimally deviate from its nominal trajectory, effectively displacing the singular region such that it is not encountered again in subsequent executions.