Structural optimization of robots and three-dimensional modeling of robot workspace

Optimizing a 6-DOF robotic mechanism that has 24 kinematic parameters is a very complex and challenging task. This study divided the optimization process into two steps, i.e., structural optimization and dimensional optimization. Moreover, this study constructed an optimal 6-DOF robotic structure based on a unique combination of an optimal 3-DOF regional structure and an optimal 3-DOF orientational structure. To search an optimal robotic structure, this study presented a general objective function called "capacity index" that reflected the effectiveness of how certain linkage length of a manipulator could generate needed reachable workspace. An optimal mechanical structure for a robot manipulator was defined if its capacity index was maximized. The optimization process started from manipulators with single DOF and two DOFs, and then extended to all possible 3-DOF robot regional structures. Optimal 3-DOF orientational structures were also derived for maximal dexterity of orientation. This study found out that the maximal capacity index for an optimal 6-DOF robotic structure to be able to reach will be equal to 4.189, and any practical design constraints or limitations will tend to reduce the capacity index. Furthermore, the optimal 6-DOF robotic structure should have six revolute joints with its regional structure and orientational structure fully decoupled. With optimal robotic structures in mind, detailed procedures for dimensional optimization of typical 6-DOF robot manipulators were provided. Finally, this study also presented a novel approach of using popular commercially-available solid modeling programs, such as Pro/EngineerRTM, to create 3D models of robot workspace.