Abstract
For affine non-linear systems, we study the effects of uncertainties in systems vector fields on decoupled linear input-output behaviour. A characterization of an allowable class of perturbations which preserve the decoupling properties of the nominal system is given. An immediate consequence of this characterization indicates that decoupling position control of rigid robotic manipulators is not robust under any perturbations in robot dynamics. The result is applied to simple hamiltonian control systems to characterize the allowable perturbation of total energy function.