Encapsulated trajectory tracking control for autonomous vehicles

The motion control of autonomous vehicles with a modular, service-oriented system architecture poses new challenges, as trajectory-planning and -execution are independent software functions. In this paper, requirements for an encapsulated trajectory tracking control are derived and it’s shown that key differences to conventional vehicles with an integrated system architecture exist, requiring additional attention during controller design. A novel, encapsulated control architecture is presented that incorporates multiple extensions and support functions, fulfilling the derived requirements. It allows the application within the modular architecture without loss of functionality or performance. The controller considers vehicle stability and enables the yaw motion as an independent degree of freedom. The concept is applied and validated within the vehicles of the UNICARagil research project, that feature the previously described system architecture to increase flexibility of application by dynamically interconnecting services based on the current use-case

Comparing Different Levels of Technical Systems for a Modular Safety Approval - Why the State of the Art Does Not Dispense with System Tests Yet

While systems in the automotive industry have become increasingly complex, the related processes require comprehensive testing to be carried out at lower levels of a system. Nevertheless, the final safety validation is still required to be carried out at the system level by automotive standards like ISO 26262. Using its guidelines for the development of automated vehicles and applying them for field operation tests has been proven to be economically unfeasible. The concept of a modular safety approval provides the opportunity to reduce the testing effort after updates and for a broader set of vehicle variants. In this paper, we present insufficiencies that occur on lower levels of hierarchy compared to the system level. Using a completely new approach, we show that errors arise due to faulty decomposition processes wherein, e.g., functions, test scenarios, risks, or requirements of a system are decomposed to the module level. Thus, we identify three main categories of errors: insufficiently functional architectures, performing the wrong tests, and performing the right tests wrongly. We provide more detailed errors and present examples from the research project UNICARagil. Finally, these findings are taken to define rules for the development and testing of modules to dispense with system tests

Systemarchitektur und Fahrmanöver zum sicheren Anhalten modularer automatisierter Fahrzeuge

Maschinelle Systeme übernehmen einen immer größer werdenden Anteil der dynamischen Fahraufgabe automatisierter Fahrzeuge. Funktionale Degradationen können die Fähigkeiten dieser Systeme negativ beeinflussen, sodass sie die Fahraufgabe nicht weiter erfüllen können. In diesen Fällen wird bei höher automatisierten Systemen die Fahraufgabe von einer maschinellen Rückfallebene übernommen. Im Rahmen des Forschungsprojekts UNICARagil wird eine modulare und dienstbasierte funktionale Fahrzeugarchitektur entwickelt, für die in diesem Beitrag die Anforderungen und die Systemarchitektur einer geeigneten funktionalen Rückfallebene vorgestellt werden und der weitere Forschungsbedarf hinsichtlich der erforderlichen Fähigkeiten der Teilfunktionen, ihrer gegenseitigen Abhängigkeiten und der Absicherung der Teil- und Gesamtfunktionen erläutert wird

Macroscopic Safety Requirements for Highly Automated Driving

The common expectation for highly automated vehicles (HAVs) is that an introduction will lead to increased road safety and a reduction in traffic fatalities—at least in relation to the mileage. However, quantizing the safety requirements is still in discussion. This paper analyzes the risk acceptance in other fields and applies the safety level on today’s traffic to derive references for acceptable risks. The focus is on macroscopic safety requirements, meaning accident rates per mileage, and not the behavior in individual driving situations. It was concluded that the acceptable risk varies according to the group involved and with the field share of automated vehicles. Increased safety of conventional driving in the future could lead to higher requirements as well. We also point out that it is not guaranteed that the given acceptable risk levels will also accepted by the user, because factors other than the accident statistics are relevant. However, as none of these risk levels can be proven before introduction, the monitoring of vehicles in the field is suggested. Despite increased research efforts in safety validation, uncertainty surrounding the safety of HAVs will remain at the time of introduction. Different introduction and risk management strategies are briefly introduced

Acceleration-Based Collision Criticality Metric for Holistic Online Safety Assessment in Automated Driving

Criticality metrics are not only essential for collision avoidance systems but also play a vital role for verification and validation of automated vehicles. With respect to the first application, criticality metrics should be real-time capable and applicable in various traffic situations. For the second application, holistic safety evaluation by criticality metrics is desired. However, existing criticality metrics hardly meet these two requirements. They are either only applicable in post-processing or only assess the safety of maneuvers in longitudinal direction. Therefore, we propose a new acceleration-based criticality metric, which is real-time capable and applicable in both longitudinal and lateral directions. The theory of the proposed criticality metric is introduced and the definition is explained according to different scenarios. A simulation platform is established to validate the criticality metric. The simulation results demonstrate that the proposed criticality metric takes all possible maneuvers into account when meeting a critical situation. Apart from the longitudinal behavior, the lateral behavior of automated vehicles can also be evaluated in real-time. Consequently, it has a wider application scope than other criticality metrics. To demonstrate its contribution to verification and validation of automated vehicles, we apply the criticality metric to a naturalistic driving dataset. The results prove that our criticality metric has a higher precision and recall than Time to Collision. Additionally, it combines the abilities of Time to Collision and Time Head Way to assess the safety of automated vehicles in the longitudinal direction. The proposed criticality metric is real-time capable and is suitable for different situations

Approach to Maintain a Safe State of an Automated Vehicle in Case of Unsafe Desired Behavior

For automated driving, higher levels of automation pose new challenges in terms of safety. In this paper, we develop a generic behavior safety framework that maintains a safe vehicle state even in case of system failures. It is applicable to different configurations of automated driving system architectures. We verify the designed generic behavior safety framework by applying it to two different architectures from both projects PRORETA 5 and UNICARagil. The previously defined safety requirements are met with both applications, which indicates that the developed generic safety framework is also valid for other configurations of automated driving systems

Real-Time Pose Graph SLAM based on Radar

This work presents a real-time pose graph based Simultaneous Localization and Mapping (SLAM) system for automotive Radar. The algorithm constructs a map from Radar detections using the Iterative Closest Point (ICP) method to match consecutive scans obtained from a single, front-facing Radar sensor. The algorithm is evaluated on a range of real-world datasets and shows mean translational errors as low as 0.62 m and demonstrates robustness on long tracks. Using a single Radar, our proposed system achieves state-of-the-art performance when compared to other Radar-based SLAM algorithms that use multiple, higher-resolution Radars

“Evaluation of an electromagnetically actuated drum brake concept”

In publications and conferences on the subject of wheel brakes, different concepts of electromechanically actuated wheel brakes can be found, as well as investigations into their suitability for the use in passenger cars. The vast majority of these brakes are disc or drum brakes, which are actuated by an electric motor. In the present publication, a brake concept is considered, that combines an electromagnetically actuated full-pad disc brake with a 10″ duo-duplex drum brake. The brake concept is researched in a project regarding brakes for autonomous shuttles and thus dimensioned using vehicle data of an example shuttle. The electromagnet was designed using finite element methods and the overall brake prototypically realized. The validation of the system design is carried out in component and system tests. The results show the suitability of the concept for the selected vehicle in terms of dynamics, installation space and energy requirements. However, there is a strong dependence of the braking torque output on the frictional sliding speed. Using hypothesis-based testing, electromagnetic effects like eddy currents are ruled out as a possible cause and the friction coefficient within the full-pad disc brake is identified as the main cause for the loss in torque. Consequently, the associated development conflict is identified and lies in the double function of the flux-carrying material in the electromagnet, which also acts as a friction partner for the braking disc

Ideal Reference Point in Planning and Control for Automated Car-Like Vehicles

The choice of the reference point in automated vehicles impacts the vehicle's driving behavior. However, this influence is often not considered for planning and control tasks. To find out where the reference point should be located best, we first consider its position to be ideal if the needed lane width on the left and right side of the planned path is equal when cornering with constant curvature. For constantly curved paths we derive the ideal reference point depending on the curvature, using the kinematics of a slip angle free bicycle model. For non-stationary cornering, we analyze different maneuvers and finally, we select the reference point on the front axle. Utilizing this knowledge, the extent of a forward moving vehicle can be reduced to a point model, which does not require the orientation of the vehicle. This enables a simple and still promising approach for collision checking, where the vehicle's needed space is approximated by only one circle around the reference point. Finally, we analyze the influence of the reference point on a lateral feed-forward controller. Thus, we confirm the previously chosen reference point on the front axle for the equally distributed needed lane width and therefore recommend its use