Active, passive, and semiactive vibration suppression by stiffness variation

This paper investigates the vibration suppression by stiffness variation. First, optimal on-off control logic for a single-degree- of-freedom variable-stiffness system is proposed. A control logic for a multiple-degree-of-freedom system with multiple variable-stiffness elements is also proposed. As an example of a variable-stiffness system, a string whose tension is controllable is studied. Numerical simulation demonstrates the effectiveness of the proposed control logic. Next, a dry friction is shown to vary the tension of a string in the same way as this active control when the longitudinal stiffness is high, realizing a passive vibration suppression. The performance of the passive system is studied. To overcome the disadvantages of the passive system, a semiactive control is proposed, that controls the frictional force. Numerical simulations and an experiment demonstrate its effectiveness and robustness, although it is primitive.