Thomas Sattel

Combining haptic human-machine interaction with predictive path planning for lane-keeping and collision avoidance systems

This paper presents a first approach for a haptic human-machine interface combined with a novel lane-keeping and collision-avoidance assistance system approach, as well as the results of a first exploration study with human test drivers. The assistance system approach is based on a potential field predictive path planning algorithm that incorporates the drivers wishes commanded by the steering wheel angle, the brake pedal or throttle, and the intended maneuver. For the design of the haptic human-machine interface the assistance torque characteristic at the handwheel is shaped and the path planning parameters are held constant. In the exploration, both driving data as well as questionnaires are evaluated. The results show good acceptance for the lane-keeping assistance while the collision avoidance assistance needs to be improved.

The importance of rotor flexibility in ultrasonic traveling wave motors

In the simulation of a typical ultrasonic traveling wave motor, usually at least four topics have to be considered: modeling the stator, the piezoceramic ring bonded to the stator, the rotor and the contact problem between stator and rotor. Although from experimental observations it is well known that rotor flexibility strongly affects the motor behavior, this has so far not been taken into account in modeling these motors. The aim of this paper is to point out the importance of rotor flexibility in an electromechanical model of an ultrasonic traveling wave motor. A motor of the plate type with one piezoceramic ring is modeled. The simulation is based on the approach suggested by Hagood, where we however incorporate rotor flexibility. The geometrical and material parameters for the model are taken from data of an industrial prototype motor. The coefficient of friction between the contact layer of the rotor and the stator is obtained from the stall torque, and the damping of the disk spring is adjusted to measured torque-speed characteristics of the motor. The steady state dynamical behavior of the model is simulated in the frequency domain. Such an analysis can be carried out much faster than the numerical integration of the equations of motion in the time domain, as originally done by Hagood. It turns out that the measured torque-speed characteristic can not be fitted if rotor flexibility is ignored, while good results are obtained if the flexibility of the rotor is included in the model.

From robotics to automotive: Lane-keeping and collision avoidance based on elastic bands

In the near future, drivers will more and more share vehicle guidance with assistance systems. This contribution provides a potential field-based approach to the underlying motion planning problem. In doing so, the concept of elastic bands, known from robotics, is extended to automotive applications. Contrary to robotic applications, extrapolation routines anticipating the motion of the surrounding traffic are incorporated in the motion planning. New in this paper is the distinction of different types of obstacles such as traffic staying in its lane and traffic intending to depart from it. Beyond that, the motion planning adapts to the drivers commands. The driver can be included in the overall control loop by means of a haptic interface generating a torque that depends on the difference of the actual steering angle and the steering angle necessary to follow the planned trajectory. However, this contribution focuses only on the underlying motion planning procedure.

Ground vehicle guidance along collision-free trajectories using elastic bands

Latest developments in automotive sensor technology promise an unbroken innovation thrust for driver assistance systems. Accordingly, future vehicles might be able to navigate autonomously. For autonomous vehicles collision avoidance systems (CAS) are essential. Key elements of CAS are automatic path planning, path following and model based estimation of the driving conditions of a CAS-equipped car. For this purpose, a path planning technique using modified elastic bands is presented. Furthermore, a possible overall CAS-structure including path following control and driving condition estimation is discussed. Finally, simulation results for an evasion maneuver are given.

On Automatic Collision Avoidance Systems

In future automotive collision avoidance systems (CAS) collision-free path planning will be required. For this reason, two possible path planning techniques are compared. The first method is based on the mathematical theory of differential games, the second method focuses on so-called elastic bands. However, the method of elastic bands is essentially modified to provide solutions in complex driving situations. Furthermore, it is shown how path planning, path following control and driving condition estimation can be embedded in a possible overall CAS-setup. Therein, driving conditions are estimated based on the characteristic velocity. Finally, simulation results for an emergency maneuver are presented.

The Contact Problem in Ultrasonic Traveling-Wave Motors

In this paper the contact mechanism between stator and rotor will be considered in detail, which plays a key role in ultrasonic motors. A planar contact model for the stator-rotor interaction in traveling-wave type ultrasonic motors is derived, including rotor flexibility and differenciating between stick and slip regions in the contact zones. The model analysis shows that depending on the motor’s operating conditions, complicated contact behavior may occur with several stick-slip subzones in each contact zone. The typical nonlinear resonance observed in ultrasonic motors can be explained with the present analysis. Both the stiffness of the contact layer and of the rotor may drastically influence the speed-torque characteristics. The results will contribute to a better understanding of the contact mechanics in ultrasonic motors.

Comparison of trajectory tracking controllers for emergency situations

Over the last years a number of different vehicle controllers has been proposed for tracking planned paths or trajectories. Most of previously published works do not compare their results with other approaches or limit the comparison to a few scenarios. Unfortunately, comparisons with existing controller concepts are very rare and a ranking is hard to establish from the literature. In this work, we rigorously compare inversion-based trajectory tracking controllers by systematically exploring the set of possible solutions when disturbances vary over time and initial states and parameters are uncertain. By using Monte-Carlo simulation, we determine the average performance and by using rapidly exploring random trees, we determine the worst-case performance, which is especially important in emergency situations when avoiding a crash is essential. The tested scenarios and the applied methodologies are documented in detail so that they serve as benchmark problems for other control concepts. The results show that the controller with smaller relative degree performs better with respect to the worst-case deviation computed by rapidly exploring random trees, while conventional simulations of random scenarios would not reveal any difference.

Towards vehicle trajectory planning for collision avoidance based on elastic bands

Vehicle safety and driver assistance systems are an active field of research. Therein, a current trend focuses on guidance systems that link the vehicle to its environment. This paper presents a potential field based guidance strategy, which supports lane keeping and evasion manoeuvres. Therein, potential fields are scaled according to the hazard levels associated to the borders of the road and to other traffic participants. Trajectories of low hazard levels are generated by means of elastic bands that sense the environment like antennae of insects. An important contribution of this predictive motion planning approach is the incorporation of moving obstacles.

An Approach to Integrate Vehicle Dynamics in Motion Planning for Advanced Driver Assistance Systems

Path planning procedures belong to the key software elements for advanced driver assistance systems including vehicle following, lane-keeping, lane-changing, or collision avoidance. One approach to realize an integrated driver assistance on the guidance level is based on an elastic band immersed in a potential field hazard map. This paper presents an extension of this elastic band path planning method, incorporating the vehicle dynamics in the elastic band. It is shown that this measure enhances the drivability of the planned paths.

Formal verification of maneuver automata for parameterized motion primitives

An increasing amount of robotic systems is developed for safety-critical scenarios, such as automated cars operating in public road traffic or robots collaborating with humans in flexible manufacturing systems. For this reason, it is important to provide methods that formally verify the safety of robotic systems. This is challenging since robots operate in continuous action spaces in partially unknown environments so that there exists no finite set of scenarios that can be verified before deployment. Verifying the safety during the operation based on the current perception of the environment is often infeasible due to the computational demand of formal verification methods. In this work, we compute sets of behaviors for parameterized motion primitives using reachability analysis, which is used to build a maneuver automaton that connects motion primitives in a safe way. Thus, the computationally expensive task of building a maneuver automaton is performed offline. The proposed analysis method provides the whole set of possible behaviors so that it can be verified whether forbidden state-space regions are avoided during the operation of the robot, to e.g. avoid colliding with obstacles. The method is applied to continuous sets of parameterized motion primitives, making it possible to verify infinitely many motions within the parameter space, which to the best knowledge of the authors has not been published before. The approach is demonstrated for collision avoidance of road vehicles.