High fidelity modeling of wear, hysteresis, and tooth cracks in strain wave gears for PHM purposes

Strain Wave Gears (SWGs) are widely used in aerospace and robotics for their high reduction ratio, low backlash, and compact design. An important field in which they will be largely used in the future is the development of compact Electromechanical Actuators (cEMA) specifically designed for electric aircraft to be implemented in Urban Air Mobility scenarios. Due to the key role played by these components in guaranteeing the passengers' safety, it is necessary to monitor their health status and estimate their remaining useful life. The application of Prognostics and Health Management (PHM) techniques requires a large amount of data, which can come from experimental tests, historical database, or simulations. The first two approaches are more effective, but they are expensive and require a lot of time. For these reasons, the third one is often chosen as suitable alternative. In this context, a two-dimensional planar equivalent model of a SWG is developed to replicate the reducer behavior in nominal and degraded operating conditions. The proposed model includes the effects of wear, hysteresis, and tooth crack on the SWG performance, and the outcomes of the simulations derived from it are compared with the literature in order to evaluate the ability of the model to replicate real behavior. The proposed model represents a first important step in the development of a fully-realized digital twin of the cEMA with a rotary output capable of replicating the system behavior in both nominal and faulty conditions.