Although serial manipulator arms modeled with rigid links show full system controllability in the joint space, this condition does not necessarily hold for flexible robotic systems. In particular, in certain robot configurations, called inaccessible robot positions, one or more of the flexibilities may not be accessed directly by the actuators. This condition may significantly deteriorate system performance as reported earlier by the authors (Tosunoglu et al., 1988, 1989). The present study addresses the relationship between the accessibility and controllability concepts and establishes accessibility as a distinct concept from controllability. Although the theoretical framework is developed for general n-link, spatial manipulators modeled with m oscillation components, example case studies demonstrate the concepts on one- and two-link arms for brevity. Specifically, it is shown that although inaccessibility and uncontrollability may coincide in certain instances (as shown on a one-link arm), counter examples may be found where an arm in an inaccessible position can simultaneously demonstrate full system controllability (as shown on a two-link arm).

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