On the Existence and Characteristics of Solution Paths at Algorithm Singularities

Abstract

Abstract The Extended Jacobian method is a popular approach for controlling a kinematically redundant arm which allows one to resolve redundancy by locally optimizing an objective function and to gain repeatability for a cyclic end effector trajectory. It is a special case of a family of methods called constraint function methods. It has been found that the occurrence of algorithmic singularities can cause severe difficulties and the advantages of the methods such as repeatability might no longer exist. The purpose of this analysis is to study the characteristics of algorithmic singularities, especially ones where only one rank is lost. We establish sufficient conditions for the existence of a joint path at an algorithmic singularity. The phenomenon of branch repeatability is shown to occur at an algorithmic singularity. We also show that the extended Jacobian method cannot successfully optimize the objective function beyond the singularity without loss of continuity of the joint derivative. Simple examples are given to demonstrate the use of our theoretical results.