Abstract: The theory and control countermeasures of active vibration control for flexible mechanisms are studied by the modal theory, and the correspondent optimal control scheme is proposed. The stabilities of the scheme is discussed. Methods to extract modal displacements and velocities from measurements of the actual displacements and velocities are investigated, in which the effects of control spillover are considered. Except that, the actual control force (moment) computation method are also presented. Finally, with the control scheme, simulations for the on-line vibrations control of an elastic four-bar path generator and the residual vibrations control of a flexible manipulator arm are carried out.

Key words: Active control, Flexible Mechanisms, Vibration