This paper rechecks the relative degree
of the end-point tracking control system of a flexible manipulator.
New added insights into the ill-defined behavior of the
relative degree are presented by constructing a perturbed truncation model.
The implications for the inverse dynamics motivate us to reformulate
the inverse dynamics based on the perturbed truncation model in
the extreme case of truncating all of the flexible modes.
New potential advantages arising from this novel formulation are investigated
for the inverse dynamics control design as well.