For a controlled structure, the changes of physical characteristics like natural
frequencies, modal damping coefficients, and what’s more on mode shapes will destabilize
the controlled system. To keep the control performance and guarantee its robustness, a new
modal control method using real-time identification is proposed to overcome the
instability of controlled structure, especially induced by the inversion of mode shape. In
this paper, a modal model of time-varying mechanical structure is supplied by an
identifier. The choice of the kind of control permits to use this time-varying model for
optimizing and self-adapting the controller. In order to supply the controller, a modal
observer is used and also updated. For illustrative purpose, this proposed methodology is
carried out on a simple but representative time-varying mechanical structure. On this
example, an inertia modification leads not only to low modal frequency shifts but also to
inversion of a mode shape. This mode shape inversion is shown to destabilize the
controlled structure when the control system is not updated. The overall procedure will be
described through simulations and performed for different operating conditions, which will
prove that mode shapes have to be precisely determined and updated in the controller and
observer to guarantee a robust modal control with high performances in spite of the
changes of structure.