Robot Manipulator Redundancy Resolution

Chapter 9QP-Based Self-Motion Planning

9.1 Introduction

Kinematically redundant manipulators are those that have more DOF than required for (specific) end-effectors' position-and-orientation tasks [62]. This implies that redundancy can also be established with respect to some particular tasks; for example, positioning only. For non-redundant manipulators, the joint motion is usually determined uniquely by a prescribed end-effector trajectory and, thus, there is no freedom left to handle secondary tasks, such as the handling of joint physical limits and environmental constraints (e.g., obstacles). In comparison, redundant manipulators have wider operational space and extra DOF to meet a number of functional constraints and performance criteria because there exist an infinite number of joint configurations as feasible solutions (corresponding to a prescribed end-effector task).

A fundamental issue in operating redundant mechanical systems is the inverse-kinematics problem (or to say, the redundancy-resolution problem) [1]. It can generally be described; “given the desired Cartesian trajectory at the manipulator end-effector, how can we generate the corresponding joint trajectory in real time ?”. By resolving the redundancy properly, the robots can avoid joint physical limits, obstacles, ...