The Electrodynamic Vibration Absorber as a Passive or Active Device

The theory of a new damper is derived and verified experimentally. The damper utilizes an electric armature elastically coupled to its field stator which is fixed to the vibrating system. The electric energy output is discharged through an electric network. The damper compares favorably to a dynamic absorber. When active feedback is utilized, much better efficiency can be obtained. Optimum tuning can be attained by relating the resonant frequency of the electric current to that of the main system. Damping is provided through the electric circuit and adjusted by varying either the resistance of the circuit or the magnetic field strength. Eliminating the spring coupling between the armature and the vibrating system results in a system similar to the Lanchester damper, with much higher efficiency. The absorber can be applied to torsional as well as unidirectional (lineal) vibrations at any practical frequency range. The experimental damper, with a mass ratio of 1/71, produced an optimum magnification factor of 10.5 comparable to a dynamic absorber at similar conditions. The theory of this passive damper is modified to account for feedback conditions. A signal proportional to the strain in the elastic support of the vibrating system is amplified and fed to the armature of the damper through the proper transfer network. Under sinusoidal force input, the experimental characteristics displayed a fairly flat response. With an armature mass of 1/340 of that of the vibrating system, a maximum magnification factor of only 4 was obtained experimentally. Both theoretical and experimental response plots are given and analyzed under different feedback conditions. The damper with feedback may be employed without external viscous damping and the frequency tuning can be achieved by the proper choice of the feedback network. Because of its construction as an electric machine, it is foreseen to be applicable in mechanical and control systems. The characteristics presented add in a detailed fashion to those reported in the literature for similar feedback applications.