A multivariable nonlinear controller is investigated for vibration sup
pression of flexible structures. The closed-loop gain matrix consists
of a varying term added to a constant term. The varying term is propor
tional to the measured signal, providing rapid cancellation of large d
eflections and maintaining low noise sensitivity. L2-stability is prov
ed, and experimental results show improvement of performance compared
to a corresponding linear controller with constant gain.