Two‐arm kinematic posture optimization for fixtureless assembly

This article focuses on finding optimal kinematic postures for two robot arms performing various assembly tasks without the aid of jigs and fixtures. The goal of the work is to identify the manipulator postures that would result in some optimum kinematic conditions for initiating a typical male‐female assembly. Specifically, the article addresses issues related to the following question: In the absence of preset jigs and fixtures, where are the optimum location in the 3‐dimensional work space and the optimum orientations of the assembly parts (therefore, the postures of the manipulators holding the parts) to perform a fixtureless assembly? First, using velocity and force ellipsoids a performance criterion is developed for the optimal kinematic posture based on constraints that are imposed by the kinematic coupling of the two robot arms as well as the environment. Next, an algorithm based on a null‐space search technique is formulated to “search” for the posture of the two‐arm system that maximizes the performance criterion within the set of postures that satisfy given constraints. Finally, the algorithm is demonstrated numerically for two planar robots performing typical fixtureless assembly operations.