Nonlinear Dynamics of an Electro-Mechanical Energy Scavenger Stefano Tornincasa*, Elvio Bonisoli*, Francesco Di Monaco*, Sandro Moos*, Maurizio Repetto**, Fabio Freschi** *Department of Production Systems and Business Economics - Politecnico di Torino, Italy **Department of Electrical Engineering - Politecnico di Torino, Italy Abstract This paper presents a very compact electro-mechanical wideband energy harvester optimized for tire applications. The energy conversion process of the device takes into account the simulation of different phenomena like: non linear dynamic and adaptive resonant behavior of the seismic mass, electromagnetic and magneto-static coupling between floating magnetic mass and coils, transfer of the generated power to an external load by means of a nonlinear circuit interface. The paper is focused on the pneumatic effects of the floating magnet sliding into a calibrated guide. A convenient choice of clearance between moving and fixed parts can be used to create an effective air brake preventing or softening shocks with end stops and to modify system dynamic. A block-oriented Simulink®, experimentally validated, model has been realized to predict scavenger device performance and to optimize design parameters. Equivalent linearized stiffness and damping factors due to pneumatic effects have been modeled in the lumped parameters system to get a simplified model and to formalize relations with the geometrical characteristics. Analysis of the effect of several nonlinearities at different vehicle speed have been performed. Keywords: energy scavenger, electro-mechanical device, adaptive resonance Introduction To power remote sensor nodes, if the batteries substitution is unadvisable, unsafe, onerous or even impossible, a possible solution is the use of energy scavenger (or energy harvester) devices. These devices are designed to recover energy from a specific source available in the destination environment. Is possible to scavenge energy from a wide set of sources as: ambient-radiation, temperature deltas, motion and vibrations. To scavenge energy from vibrations are typically used resonant spring mass systems linked to piezoelectric, magneto-mechanic or electrostatic generators [1-2]. A sensor node installed inside a tire, where is obviously impossible to bring power through wires, is a suitable application for an energy scavenger device, if a battery enough capacious to power the sensor for its whole lifetime is too big or too heavy. In fact during the wheel rotation, variation in acceleration components can induce vibrations in properly designed parts and is possible to exploit these vibrations to scavenge and accumulate energy. Due to the very high stresses that a component installed in a tire has to resist, in this work has been chosen to design a magneto-mechanic (instead of electrostatic or piezoelectric) energy scavenger device. Since the tire can be subjected to an extended range of revolving speed, a challenge to overcome is to properly design an energy scavenger device able to exploit a wide range of frequencies so to obtain an acceptable power output in many different working conditions. T. Proulx (ed.), Modal Analysis Topics, Volume 3, Conference Proceedings of the Society for Experimental Mechanics Series 6, 339 DOI 10.1007/978-1-4419-9299-4_30, © The Society for Experimental Mechanics, Inc. 2011
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