CORDIS - EU research results

Health On Line Monitoring for Electro-mechanical actuator Safety

Final Report Summary - HOLMES (Health On Line Monitoring for Electro-mechanical actuator Safety)

Executive Summary:
The problem of detecting faults in electromechanical actuators (EMA) has been tackled by many scientists over the last 20 years and some researches can be found in literature.
The replacement of hydraulic systems with the implementation of EMAs on flight control actuation systems of both A/C and H/C can lead to many advantages but, since the mechanical jam of such a system has to be considered as a possible and high critical event, research activities have to pay attention to the compliance with the operational reliability and safety requirements. Two major approaches have been pursued: model based and model free methods. Model-free methods are preferred than model-based methods, since the latter’s require a mathematical model of the system than it is often difficult to design with sufficient accuracy. The model-free methods are based only on signal processing of measured variables and they are focused on the goal of rising alarms and classify the faults. However, the trend in current research is to combine the two methodologies, to gain the benefits of both worlds. Such later approach was demonstrated to be promising for the early identification of mechanical failure of ballscrews, gears and bearings. Such results have to further developed in order to be used in actual applications.

Project Context and Objectives:
The project aimed to develop a reliable tool for the health monitoring of electro-mechanical actuators (EMAs). Use of sensors was already successfully proved by Umbra for the detection of the ballscrew failures but the challenge was to rely on components that are basic on an EMA like electric motors, position sensors, motor commutation devices. A promising parameter like the phase electric motor current was evaluated as well as others. The reliability and safety of the EMA will be improved without any penalty in terms of weight and envelope.

Project Results:
The project was split in the work packages below:
- WP2 was dedicated to the analysis and evaluation of the state of the art. In the first part of this work
package a broad survey has been performed covering literature studies and other project activities about the state of the art of health monitoring systems and methods for electro-mechanical actuator in aerospace applications. The attention will be focused on mechanical drive train, including screw drives, gears and bearings. Then, some works of this WP will be dedicated to the investigation on possible failures of ballscrew, gears, and bearings and to the identification of relevant variables to be monitored and recorded.
- WP3 included all experimental activities which are preparatory for the development of the health
monitoring system. A test bench has been adapted considering indications got from WP2’s activities. At the same time test specimen have been prepared and the test plan defined. At first, not-defected specimen have been characterized.
Then, failures have been generated on specimen to be tested. The careful analysis of the DO-160 standard led to the definition of low-temperature tests that have been performed.
- WP4 included the analysis of results of the experimental campaign and the development of simulation tools for ballscrews, gears and bearings, and the design of model-based and model free algorithms for FDI (i.e. Failure Detection and Isolation). After the definition of the mathematical description of faults scenarios, several approaches have been considered and evaluated for the design of the model-based algorithm (fault detection based on parameter estimation, algorithms based on measurement observers, statistical approach for alarm generation). At the same time, model-free algorithms have been designed. Final decisions consisted in an observer like model-based fault detection algorithm, and a data-drive solution which leverages machine learning algorithms.
- In WP5 the developed algorithms were embedded in a prototypal monitoring software.
The main milestones have been:
- the satisfactory results of the tests which have demonstrated that mechanical failures can be detected with significant confidence by the selected model approach and selected monitoring parameters;
- the issue of the software developed from the selected algorithms.
The promising results of the project have to be further developed and tested in order to be implemented in aerospace applications.

Potential Impact:
The results of HOLMES project can extend the application of electromechanical actuators in aviation. Such technology is considered to provide environmental benefits in comparison to the current actuation technology based on hydraulic actuators. Health monitoring of the electromechanical system may provide benefits on safety, availability and ownership cost in aviation. The indication of a forthcoming failure allows to avoid critical conditions for the flight and to restore the full operability without any sudden disruption of the service. Further and deeper studies are necessary in order to confirm the current data and validate a product for aeronautical applications.

List of Websites:
Public website is not foreseen for HOLMES project