Kinematic Design Method for Rail-Guided Robotic Arms

For special purpose robotic arms, such as a rail mounted ballast-water tank inspection arm, specific needs require special designs. Currently, there is no method to efficiently design robotic arms that can handle not quantifiable requirements. In this paper, an efficient method for the design and evaluation of the kinematics of manipulator arms on mobile platforms, with certain reach requirements within a limited space, is presented. First, the design space for kinematic arm structures is analyzed and narrowed down by a set of design rules. Second, key test locations in the workspace are determined and reduced based on, for example, relative positions and symmetry. Third, an algorithm is made to solve the inverse kinematics problem in an iterative way, using a virtual elastic wrench on the end effector to control the candidate structure toward its desired pose. The algorithm evaluates the remaining candidate manipulator structures for every required end-effector positions in the reduced set. This method strongly reduces the search space with respect to brute force methods and yields a design that is guaranteed to meet specifications. This method is applied to the use case of a rail-guided robot for ballast-water tank inspection. The resulting manipulator design has been built and the proof of concept has been successfully evaluated in a ballast-water tank replica.