In this paper, an electro-mechanical system based on the "smart spring" concept is analyzed [1]. The "smart spring" existing stiffness control capabilities for rotorcraft vibration attenuation are extended to work as an energy harvesting device. The device is targeted to supplement or potentially replace the conventional lead-lag damper in helicopters. It is designed to provide the necessary attenuation for the lead-lag blade mode and, simultaneously, harvest electrical energy inside the rotating frame. The "smart spring" concept consists of two load paths, each represented by a mechanical spring. The secondary load path includes a damping element and a piezoelectric actuator, as indicated in Figure 1. The basic principle of the concept is to allow the secondary load path to engage and disengage through a friction-based mechanism actuated by a piezoelectric element. In the present work, a control principle based on an analogy between the "smart spring" and the control algorithm known as Synchronized Switch Damping on Inductor (SSDI) is analyzed throughout numerical simulations [2]. The results indicate the possibility to generate large damping forces when the SSDI control algorithm is used in the "smart spring". An optimized "smart spring" design is then integrated into a simple 1 Degree of Freedom (DOF) model of the lead lag damper of a helicopter to provide an additional damping element to the conventional device. Simulations that use the "smart spring" damper as an supplementary damping element, thus supplying only 8% of the total damping, show that a mean power of up to 10 W can be harvested in the 130 kn forward flight condition. The maximum power of the presented device is currently limited by a pre-set maximum clamping force of the friction based clamping of the "smart spring". The "smart spring" energy harvester would potentially be integrated into a multi-functional device that replaces the lead lag damper element, producing peak mean power outputs of up to 100 W per blade.

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Conference 42nd European Rotorcraft Forum 2016
Scholle, P. (Patrick), Nitzsche, F, Vieira, W. (Wander), & Sinapius, M. (Michael). (2016). Energy harvesting by means of stiffness variable spring device. In 42nd European Rotorcraft Forum 2016 (pp. 1416–1426).