When designing a control system for vibration suppression of flexible
structures using modal control strategy, one must know the modal displ
acements and velocities of the controlled modes. If the vibration cont
rol forces are designed based on inaccurate modal states, the closed-l
oop performance of the vibration control system will be degraded depen
ding on the extent of the modal filter errors. In this study, the effe
ct of modal filter errors on the vibration control characteristics of
flexible structures is analyzed for IMSC (Independent Modal Space Cont
rol). A Lyapunov asymptotic stability condition that depends on the ma
gnitude of the modal filter errors is derived. The extent of the respo
nse deviation of the closed-loop system is also derived and evaluated
using operator techniques. The extent of the response deviation is fou
nd to be proportional to the magnitude of the modal filter errors.