  In this paper, we incorporate velocity observer design into the virtual
decomposition control (VDC) strategy of an $n$-DoF open chain robotic
manipulator. Descending from the VDC strategy, the proposed design is based on
decomposing the $n$-DoF manipulator into subsystems, i.e., rigid links and
joints, for which the decentralized controller-observer implementation can be
done locally. Similar to VDC, the combined controller-observer design is
passivity-based, and we show that it achieves semiglobal exponential
convergence of the tracking error. The convergence analysis is carried out
using Lyapunov functions based on the observer and controller error dynamics.
The proposed design is demonstrated in a simulation study of a 2-DoF open chain
robotic manipulator in the vertical plane.
