Improvement of manufacturing workcell layout design using weighted isotropy metrics

Abstract

For decades manufacturing companies have endeavored to develop more versatile, space-efficient, and productive assembly lines. The design of kinematically redundant robotic manipulators and their workcells are a key component in this process and have become an increasingly popular 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 and placed to achieve the kinematic fitness levels required to perform their numerous intended tasks. The optimization of manipulator placement to maximize workcell efficiency has been studied at great length. A majority of the previous placement optimization research focuses on the use fitness measures which quantify kinematic performance criteria such as motion isotropy, end-effector velocity and precision, and time-optimality. Most of these kinematic fitness measures, however, fail to capture effect of dynamics on manipulator performance levels and workcell efficiency. These dynamics considerations are especially important in tasks that involve high accelerations or large manipulator payloads, a case which typifies most modern manufacturing plants. In this paper we investigate the incorporation of dynamics into the calculation of kinematic isotropy. We will use a torque-weighted isotropy measure as a fitness metric for redundant manipulators performing tasks which require high accelerations or the handling heavy payloads. We will employ this metric as part of a multiobjective function for a manipulator placement and workcell size reduction problem. The effectiveness of the torque-weighted isotropy in design optimization will be demonstrated by decreasing the total floor-space of a workcell while maintaining kinematic isotropy and adhering to manipulator torque limits.