Minimum Dynamics Parameters of Tree Structure Robot Models

Abstract

This article presents a method to determine minimum dynamics parameters of tree structure robots. The minimum dynamics parameters were defined as a minimum set of constant parameters, not containing the zero element, and which are sufficient to calculate the dynamic model of the robot. The determination of the minimum dynamics parameters contributes to reducing the computational requirements of the robot dynamic models, and it also increases the robustness of the parameter identification process. The presented method is based on the use of recursive Newton-Euler formulations and a concept, ‘τ_i(i-th joint torque)-identifiability’ which was used recently for the determination of the minimum dynamics parameters of general serial robots by the authors. We introduced a branch which is defined as a serial link structure for the systematic analysis of tree structure robots. As the result, we can assume that the tree structure robot consists of the branches which are serial links. The motion equation of branchs is the same to that of the serial robots except for the initial and terminal conditions. Therefore, the minimum dynamics parameters of the tree structure robot can be obtained by regrouping the original dynamics parameters of the links recurrently from the tip side branch to the base side branch. The regrouping method allows us to determine all the minimum dynamics parameters of the tree structure robots completely regardless of the values of geometric parameters. To illustrate the application of the method, a robot with two fingers is examined.