Comparative analysis of kinematic redundancy resolution techniques in case of hierarchical tasks

Redundancy has been a matter of cynosure to researchers in the field of robotics. The aim of this paper is to explore by numerical simulation how to take advantage of kinematic redundancy in managing the priority and interactions between the robot’s main task and any additional tasks/constraints. Doing so, better performance will be obtained in executing desired tasks in real-life applications. Different types of redundancy that may arise during task execution are identified and studied at three levels: the robotic system, the robot-environment interaction and the sensory tools in use. The various kinematic redundancy resolution techniques are grouped into four control groups (partitioned, commutative, hybrid and hierarchical), and compared in controlling two different robots while executing several simultaneous tasks with specific hierarchy and priority. The behavior of two well-known serial manipulators of different types, namely the 4R planar robot and the LWR4+ robot, is investigated for hierarchical tasks with insufficient number of degrees of freedom for task execution. Several simulations of task execution are carried out to evaluate and compare the performances of the two robots under different redundancy resolution techniques. The objectives of this study to better interpret the cons and pros of each control method and then determine the most appropriate control technique. The obtained results can be used to provide important guidelines for the future development of more plausible redundancy resolution techniques.