Hybrid electromagnetic shunt damper with Coulomb friction and negative impedance converter

Abstract

Electromagnetic shunt damper (EMSD) offers flexible tunability of linear damping. The low damping force-to-mass ratio of the EMSD, however, hinders those applications which require large damping force. Adding a negative impedance shunt in EMSD circuit can increase its damping force and broaden its effective frequency range at the expense of causing possible instabilities in the control circuit. On the other hand, Coulomb friction damper (FD) can offer a higher damping force-to-mass ratio than EMSD but it is difficult to be precisely controlled due to its nonlinear characteristics and excessive frequency sensitivity. This paper examines, both theoretically and experimentally, two types of hybrid dampers: one combining an EMSD and a Coulomb friction damper (EMSD+FD), and the other EMSD with a voltage negative impedance converter (EMSD+VNIC). Through proper control of the additional damping arising from FD and VNIC, the problem of unstable ESMD+VNIC and the excessive frequency sensitivity of the FD are alleviated. A prototype of EMSD+VNIC+FD is built and tested. The damping force provided by the FD in the prototype is varied by adjusting the normal force applied by a compression spring, while that from the EMSD+VNIC is controlled by adjusting the shunt circuit impedance with a variable resistor. The maximized tunability of the two enhancement methods provides a ninefold increase of the tunable damping range and a sixfold increase of the damping force-to-mass ratio of the EMSD. The proposed EMSD+VNIC+FD is finally applied and tested experimentally to achieve H∞ optimization of a ground-hooked dynamic vibration absorber for the minimization of resonant vibration of a single-degree-of-freedom system.