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Modular or re-configurable robots have been studied and developed over two decades. Most researches focus on mechatronic interfaces and re-configurable capabilities. However, less attention has been paid to dynamics and control. Consequently, the control performance of a modular robot has never been comparable with an integrated robot, due to the lack of proper handling of the dynamic interactions among the modules. In this paper, the application of the virtual decomposition control to modular robot manipulators is discussed. A high-speed databus with a data rate of 100 Mbps is used for necessary information exchange among the modules. The dynamics based control is fully handled by the local embedded controllers, whereas the host computer handles the kinematics related computation. The stability of the entire robot is rigorously guaranteed. This research aims at giving the modular robots the comparable control performance as the integrated robots, while keeping the fundamental feasibilities such as low cost for mass production, high flexibility, and easy use and expansion.

While versatility and flexibility make modular and reconfigurable robots particularly suitable for applications in unstructured environments, the use of embedded electronics and local computers imposes an inherent limitation on control performance and payload capability. The virtual decomposition control (VDC) supported with a high-speed communication system has been suggested to effectively handle the dynamics and control issues aimed at allowing modular and reconfigurable robots to have the same control performance as integrated robots. In this paper, the payload capability issue is addressed by using a preloaded torsional spring to counter-balance static torques caused by gravity. Brief concept on spring design is presented, together with a review on system structure, communication mechanism, and VDC algorithms.