Robotic posture optimization and control is an important issue for industrial applications, particularly for the automobile assembly line automation workcells. The optimal posture means that a robot reaches the best configuration in order to operate on a force-related task. It can be modeled as an even joint-torque distribution problem. Through the model, four possible potential functions are developed for the posture optimization in a redundant robotic system. One of the four shows higher effectiveness than others in a simulation study. These potential functions can be more suitably applied to a dual-redundant robotic system for its multi-subtask optimization aided by a nonlinear null space control scheme for the subtask weighting factors determination.