Virtual Decomposition Control for Modular Robot Manipulators

Abstract Virtual decomposition control (VDC) is one of the most efficient approaches toward precision control of complex robots. The VDC approach uses subsystem (such as links and joints) dynamics with parametric uncertainty to construct model-based feedforward compensation terms and guarantees the stability of the entire complex robot with mathematical certainty, leading to precise motion/force tracking control with the control bandwidth being independent of the feedback control gains. The VDC approach can be naturally applied to modular robot manipulators to overcome their long-standing problem of lacking control precision in coordinated motion. In this paper, with respect to a typical module comprised of two links and one joint, the control equations of VDC are given and the virtual stability, a necessary and sufficient condition to ensure the stability of the entire robot, is proven. The experiment result yields unprecedented motion tracking precision for a one-module robot using a harmonic drive with significant friction. The ratio of the maximum position tracking error to the maximum velocity reaches 0.00024 (s).