Improvement of kinematically redundant manipulator design and placement using torque-weighted isotropy measures

As manufacturing companies endeavor to design more versatile, energy-efficient, and productive assembly lines, the design and employment of kinematically redundant robotic manipulators has become an increasingly important research focus. Redundant manipulators can perform more complex and a greater variety of tasks than their non-redundant counterparts, but this increased utility demands that manipulators be carefully designed to achieve the kinematic fitness level required to perform their numerous intended tasks. The optimization of redundant manipulators to maximize design fitness measures such as motion isotropy has been studied at great length, but much of the previous work focuses solely on kinematic considerations such as end-effector velocity and precision, which are adequate measures for light-duty, low-energy tasks. Optimizing manipulators for heavy-duty tasks, however, demands the incorporation of dynamics into these isotropy measures to ensure that large manipulator payloads and accelerations can be handled without damaging actuators or consuming exorbitant amounts of energy. In this paper we investigate the incorporation of dynamic torque limitations into the calculation of kinematic isotropy. We will use a torque-weighted isotropy measure as a fitness metric for redundant manipulators performing tasks that require high torque and energy consumption. We will employ this metric as a multiobjective cost function for both morphological design and manipulator placement optimization problems. The effectiveness of the torque-weighted isotropy in design optimization is demonstrated by decreasing total energy consumption and maintaining adequate global isotropy for heavy-duty manufacturing tasks.