High fidelity model for efficiency calculation of ball screws for flight control actuators

Over the past decades efforts have been made to introduce electro-mechanical actuators (EMAs) into the aircrafts primary flight control field, to substitute the electro-hydraulic actuators (EHSAs). The main problem which hinders a wider use of EMAs is their seizure probability, which is too high for flight control. To overcome this issue several solutions have been proposed, resulting in complex and heavy systems with no practical application. An innovative approach is to monitor the actuator health state through feature analysis using effective prognostic algorithms. The need for a high-fidelity model is then paramount. In this study, basing on a typical architecture of an EMA, a detailed analysis of the developed dynamic non-linear ball screw model is presented The backlash, friction parameters, a model of the rolling/sliding behaviour of a ball with rolling friction are taken into account, contact stiffness and preload are introduced. A discussion is presented on the results of a sensitivity analysis on the efficiency of the mechanism with respect to the above mentioned characteristic parameters under different operating conditions. The model and the results of the sensitivity analysis can be used to better understand the physics within the actuator and the ensuing fault-to-failure mechanisms which are needed for developing more efficient prognostic algorithms.