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Experimental identification of mechanical nonlinearities in a proof mass actuator

: Borgo, Mattia Dal; Lapiccirella, Giovanni; Rohlfing, Jens; Tehrani, Maryam Ghandchi; Elliott, John Stephen

The International Institute of Acoustics and Vibration -IIAV-:
25th International Congress on Sound and Vibration, ICSV 2018. Vol.1 : Hiroshima calling; Hiroshima, Japan, 8 - 12 July 2018
Red Hook/NY: Curran Associates, 2018
ISBN: 978-1-5108-6845-8
International Congress on Sound and Vibration (ICSV) <25, 2018, Hiroshima>
Conference Paper
Fraunhofer IBP ()

This paper presents an experimental study of the nonlinear dynamics of an inertial or proof mass actuator used in active vibration control. A notable strategy to exploit inertial actuators is to implement them as active damping devices in velocity feedback controllers. The purpose is to add a certain quantity of artificial viscous damping into the structure in order to reduce its level of vibration, particularly in the regions of its resonances. Since the control force on the structure is generated by accelerating the proof mass, controlling low frequency motions or large amplitude vibrations may require a very long stroke for the proof mass. Hence, the actuator may operate in a nonlinear regime of motion. A major drawback of implementing velocity feedback loops with inertial actuators is that they are only conditionally stable. Moreover, the nonlinearity associated with large amplitude motions can further reduce the stability margin of the control loop. This motivates for identifying the nonlinear model parameters of the inertial actuator when subjected to large amplitude motion. Firstly, the experimental set-up used for conducting the characterisation is shown. Secondly, the underlying linear model parameters of the actuator are identified for small excitation signals. Finally, the nonlinear behaviour of the actuator is investigated and the nonlinear model parameters are identified using the restoring force method. It is demonstrated that the proposed methodology allows identifying, qualifying and quantifying different sources of nonlinear actuator dynamics. It is observed that for the actuator investigated in this study, the transduction coupling factor is not constant but depends on the proof mass displacement, which is a source of nonlinearity even if the actuator is operated well below its stroke limit. Conversely, the suspension behaves almost linearly even at high amplitude oscillations.