## 3 Modelling and Simulation of an Aircraft Electric Braking System
### Electric Braking System Simulation  
For developing an appropriate reasoner for the EBS, a substantial amount of data is required in order to train the system to detect any anomalies. An EBS model was provided by [19], developed in the MATLAB/Simulink environment with Simscape components. The model employs a brushless DC motor to actuate the EMA in the aircraft's single EBS with ABS included serving the purpose of providing relevant data for training the reasoner. The environment in which the simulation is working is on ideal conditions, i.e., no external or environmental conditions are affecting the braking. The model is a simple representation of a single electromechanical actuator providing the necessary braking force to an aircraft. An ABS system is included in the model to give the simulation a more realistic approach. The model used has three main layers, starting from the overall aircraft speed calculation layer, the ABS controller, and the EMA layer. An overview of the model is found in Figure 1.  
A DC brushed motor block from the Simscape environment provides electric and torque parameters useful for the model. Usually, a four-actuator brake per wheel would be used in real applications, increasing the system redundancy and robustness. The failure of one actuator on a four-EMA system will certainly reduce the effects on aircraft braking, but the purpose of having this one-EMA model is to obtain more visual and impactful information for data analysis [20]. A number of sensors are integrated into the model to verify that the components are performing their intended functions, evaluate the EBS performance as a whole, and detect abnormal conditions. Temperature, torque and force sensors are included in the model and are the main source of data for the reasoner. Starting with temperature, an electric motor overheating may occur due to a number of causes mentioned previously, such as jamming, bearing and winding failures, over-voltage or other poor environmental conditions [21]. A force sensor is integrated into the model to evaluate the actuator performance and the force applied to the brake. Torque sensors are also located in the leadscrew, and it is used to gauge the torque provided by the EMA electric motor. Other specific resultant data obtained from the model are the brake pressure, resultant torque (difference between wheel torque and brake torque), aircraft and wheel velocity, wheel slip and stopping distance. Table 2 shows a list of signals and data obtained from the model. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Component** & **Failure** & **Failure Effects** & **Critical Assessment** \\ \hline \multirow{3}{*}{Electric Motor (EMA)} & Winding Damage & Overheating & \multirow{3}{*}{Catastrophic} \\  & Jamming & Loss of Torque & \\  & Overload & & \\ \hline \multirow{3}{*}{Electrical Wiring} & Open Circuit & Partial/Total Loss of & \multirow{3}{*}{Catastrophic} \\  & Short Circuit & Power & \\  & Intermittent & Thermal Runaway & \\  & Open/Short Circuit & & \\ \hline \multirow{3}{*}{Leadscrew (EMA)} & Worm-Out Threading & Control Loss of the & \multirow{3}{*}{Catastrophic} \\  & Structural Damage & & \\ \cline{1-1} \cline{3-4}  & \multirow{2}{*}{Calibration Faults} & Incorrect Sensor & \multirow{2}{*}{Major} \\ \cline{1-1} \cline{3-4}  & & Readings & \\ \cline{1-1} \cline{3-4}  & Bias Fault & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Simplified FMECA from an EBS. The model uses generic values for the simulation to generate useful data for the reasoner. Some parameters used include the initial aircraft linear velocity of 88 m/s, landing mass of 8000 kg, wheel radius of 0.34 m, and maximum brake pressure of 30,000 Pa. \begin{table}
\begin{tabular}{c} \hline \hline
**Data** \\ \hline Braking Force \\ Wheel Slip \\ Electric Motor Temperature \\ Motor Shaft Angular Displacement \\ Wheel Angular Speed \\ Aircraft Speed \\ Stopping Distance \\ Brake Signal \\ Resultant Torque \\ Motor Power \\ Brake Torque \\ Tire Torque \\ Shaft Speed \\ \hline \hline \end{tabular}
\end{table}