On the inherent characteristics of the dynamics of rigid link robot manipulators

Abstract

A method to determine the inherent characteristics of the nonlinear dynamics of open-loop chain robot manipulators with rigid links is developed using the trajectory pattern method. The method is based on the selection of a basic trajectory pattern and examining the corresponding inverse dynamics model. The trajectory pattern employed in the present study is synthesized with a fundamental sinusoidal time function and its second harmonic. This basic trajectory is appropriate since it corresponds to one of the most basic robot manipulator motions. The inherent characteristics of the dynamics of a manipulator is studied by examining the harmonic content of the actuating torques necessary for open-loop tracking of the selected trajectory pattern, and the relative significance of each harmonic. The harmonic content and the relative contribution of each harmonic are shown to be functions of the length of the path of motion in the joint coordinate space, path positioning, and the fundamental frequency of the trajectory, but independent of the number of degrees-of-freedom of the manipulator. The study provides the basis for the development of systematic approaches to path and trajectory planning from the vibration and control points of view, and design of manipulators with superior dynamic performance. As an example, the characteristics of the dynamics of a spatial 3R manipulator is investigated.