Distributed Control Architecture for Self-reconfigurable Manipulators

In recent years self-reconfigurable modular robots have gained increasing interest from part of the international robotic community. Although recent robots of this type are characterized by advanced electro-mechanical designs, the development of their supporting control techniques have only registered strong results in the field of locomotion problems, while the manipulation capabilities of existing systems still appear to be quite limited. Aiming to provide a contribution along this latter direction, in this paper we propose a computationally distributed technique for controlling the motion of any tree-structured chain resulting from reconfiguration in its operational space. The presented strategy, which could actually be adopted when dealing with any kind of chain-based modular robotic system, turns out to be particularly well suited to self-reconfigurable structures for three main reasons: (i) it is not based on any explicit role assignment; all of the modules can be added, removed or exchanged online as required, with no impact on the overall control architecture; (ii) each module has only a very limited set of local information that must be known a priori and can be totally unaware of the remaining part of the chain; (iii) no external centralized controller is necessary; basic local processing and communication units onboard every module and a simple man—machine interface providing high-level commands are enough. A global self-coordinating behavior is automatically exhibited by the proposed technique at power-on or immediately after any configuration change as the result of a number of repeated data exchanges, performed online along the chain at every sampling interval. Although achievable performances depend on the available communication bandwidth, the convergence towards a final position error of zero is, however, always guaranteed. Moreover, because the computational burden required by every module is extremely light, the proposed technique represents an effective control solution that can be easily implemented onboard many of the low-cost and small control platforms available on existing self-reconfigurable robots.