  In this paper, a new control scheme, called as additive-decomposition-based
tracking control, is proposed to solve the output feedback tracking problem for
a class of systems with measurable nonlinearities and unknown disturbances. By
the additive decomposition, the output feedback tracking task for the
considered nonlinear system is decomposed into three independent subtasks: a
pure tracking subtask for a linear time invariant (LTI) system, a pure
rejection subtask for another LTI system and a stabilization subtask for a
nonlinear system. By benefiting from the decomposition, the proposed
additive-decomposition-based tracking control scheme i) can give a potential
way to avoid conflict among tracking performance, rejection performance and
robustness, and ii) can mix both design in time domain and frequency domain for
one controller design. To demonstrate the effectiveness, the output feedback
tracking problem for a single-link robot arm subject to a sinusoidal or a
general disturbance is solved respectively, where the transfer function method
for tracking and rejection and backstepping method for stabilization are
applied together to the design.
