Mjukvaruutveckling av ett hastighetsberoende reglersystem för den elektriska styrningen av ett fordon styrt med joysticks

Abstract: The technology has advanced but the vehicle industry has not evolved at the same pace. Mechanical constructions with a steering wheel are still being used to control the steering of cars. The mechanical construction makes it harder to implement autonomous features, it adds weight and takes up space. It is commonly known that the steering wheel has been along since the early days of the car but is it still, with all this technological development, the best way of steering a vehicle? In this thesis, a control system for an electrical steering of a vehicle was developed. The vehicle was using two joysticks to steer and since these two have a lower range of motion than a normal steering wheel a system that makes it possible to steer the vehicle in a safe way at various speeds was developed. The control system was created by analysing the physical system and approximating mathematical models. Since the dynamics changes when the friction between the wheels and the ground changes several models that operates in different speed intervals were made. Thereafter, a PID parameters were adapted to get optimal step responses. The implementation succeeded but it was proven that the servo that created the turning of the wheels was too weak to achieve a natural steering. By analysing which angles of the wheels that are needed at different speeds and how cars today are constructed a mathematical function where the maximum angle of the wheels decreases with increased speed was developed. In addition, the closer the steering controllers are to the middle point of their range of motion the more is the sensitivity decreased when the speed is increased. This makes it possible to drive straight ahead without small unintended movements in the hands affecting the movement of the vehicle while it is also possible to make sudden evasive manoeuvres. A VR-environment made to scale was created to test this system. This test was successful but the system will however need to be tested in a real situation to be able to assure its suitability. To create a natural steering for the vehicle force feedback from the wheels to the steering controllers is necessary. This limits the positions of the steering controllers if the desired wheel angle cannot be achieved as well as making it possible for the driver to feel the road surface. A theoretical design was made but due to delays in the mechanical construction implemented by a mechanical engineer this could not be implemented within the frame of the thesis. This thesis has mainly been focusing on functionality but some safety functions have been implemented and tested with successful results. In addition, a theoretical study regarding redundancy was performed to facilitate future implementation.