Velocity degeneracy determination for the kinematically redundant CSA/ISE STEAR testbed manipulator

The Canadian Space Agency (CSA)/International Submarine Engineering (ISE) STEAR Testbed Manipulator (STM) is a ground-based manipulator similar to the arms of the Special Purpose Dextrous Manipulator (SPDM) being built for the International Space Station (ISS). This work presents the determination of the velocity-degenerate (singular) configurations for the STM, a system comprised of two seven-jointed redundant manipulators. The two “arms” of the STM are mirror images of one another. The analysis presented is for the STM-1 or “right” arm, but it applies to the STM-2 or “left” arm since they are mirror images and have similar dimensions and joint ranges. A methodology based on reciprocity of screws is used to identify all configurations causing one degree-of-freedom (DOF) instantaneous motion loss in the STM. It is shown that there are five families of two-condition configurations resulting in a single DOF loss for manipulators kinematically similar to the STM-1. Reciprocal screws characterizing the lost motion DOF for each of the degenerate configurations are derived. Analysis of the velocity degeneracies shows that for the STM-1 dimensions and joint limits, only four of the five velocity-degenerate configurations are feasible.