## 2 Collision Avoidance System
### Autonomous Manoeuvring Module  
After the risk assessment, the system decides whether or not some action is required to avoid a collision by comparing the different possible options. Then, the automated vehicle controls let the manoeuvre be performed should the driver not react in the right way. In this sense, within the collision avoidance system, the obstacle detection algorithm acts as a high-level layer that generates orders to the low-level layer that acts on the vehicle's controls if necessary. Most of the collision avoidance systems developed use brakes or speed reduction as the main action [59; 60]. However, in many situations this action is not enough or is not the most appropriate one, and the control system has to additionally take control of the steering wheel in order to avoid the accident. The developed vehicle control architecture has been implemented and installed in a Citroen C3 Pluriel testbed vehicle that equips an automatic gearbox, whose actuators (accelerator, brake and steering wheel) have been automated and prepared to be controlled from the onboard collision avoidance system. The vehicle equips an electronically actuated throttle. The engine central unit controls the fuel inlet by considering the voltage signal that it receives depending on the accelerator position. The solution used is to bypass the electrical signal given from the pedal by one generated from an Advantech \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Results** & **Average value (m)** & **Standard deviation (m)** &
\begin{tabular}{c} **Difference between model** \\ **and experimental data** \\ \end{tabular} \\ \hline \(D_{LC\_min\,1}\) & 22.95 & - & \(-\)11.12\% \\ \(D_{LC\_min\,2}\) & 23.90 & - & \(-\)7.44\% \\ \(D_{LC\_min\,3}\) & 21.90 & - & \(-\)15.18\% \\ Experimental data & 25.82 & 5.33 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Distance of the lane change manoeuvre at 50 km/h. USB-4711A acquisition card. To switch between the manual action and autonomous one, a switching relay is used. The vehicle brake has no electric power assistance and the solution that has been implemented for automating this system is direct action on the brake pedal via an external actuator. The braking module consists of a set of a Maxon RE35 DC motor and an ENC HEDL 5540 encoder, controlled by the Maxon EPOS 24/5 position controller that receives the target from the low-level control system. The motor acts on a pulley that moves the pedal. The speed control loop is closed by the speed measurement from the vehicle CAN bus. On the other hand, the steering system is electrically assisted. This system consists of an electric motor attached to the steering rack through a gear. This motor exerts a power over the steering that is proportional to the power exerted by the driver over the steering wheel, measured through a torque sensor located in the steering bar. This signal is received by a control/power controller that sends a PWM signal to assist the steering movement so that very little effort is required of the driver and this system has been used for automating the steering system of the vehicle. The control unit generates a signal which passes through the Maxon ADS 50/10 4-Q-DC Servo amplifier that is responsible for controlling the vehicle steering motor. The feedback loop control is performed through the signal provided by the wheel rotation sensor included in the steering column. Switching between manual and automatic control is performed by a power relay box. A central unit manages the vehicle actuators in order to comply with the commands sent by the high-level controllers. This is a low-level layer that is able to receive signals from different sources. This automation architecture makes it possible to control the vehicle by considering signals provided by the collision avoidance system or other inputs for autonomous driving. Two low-level control systems have been designed in order to satisfy the mission of the actuator control: steering controller and speed controller.