Motion constraints for self-driving vehicles during safe stop maneuvers : A proprietary method and a modification of an existing method for finding speed limitations
Abstract: At any given moment, self-driving vehicles need to be able to perform a safe stop maneuver in order to come to a complete stop in case of an emergency. It is important to find the maximum allowed entry speed in order to follow the given emergency path and stop in time without losing grip or rolling over. A new method is developed for this purpose and compared to an existing method developed by Joseph Funke and Christian Gerdes.It is found that the new method is more general but does not always converge to a solution for bad guesses and extreme paths. Also, the existing method cannot determine the initial speed for all paths. The increased generality lies in optimizing the emergency path given by a safe zone and considering different friction coefficients in lateral and longitudinal directions. Plots are presented visualizing the maximum speed´s dependence of various parameters for a specific path. The software CarMaker by IPG Automotive is used to validate the results for the developed method. The simulations done show that the method works well for paths in two dimensions but limits the initial speed more than necessary in three dimensions. Both methods find the accelerations needed at every point which may be translated into control signals as an additional use. Methods of knowing the friction coefficients in advance are also discussed.
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