Automatic path tracking using linear quadratic control theory

The authors conducted a study of automatic path tracking performance in the automated highway system (AHS) public trials that were carried out in Japan in 1996. A comparison was made of proportional-plus-derivative (PD) control and linear quadratic (LQ) control as two potential control systems. Because the PD control system lacked state feedback of yaw motion, the interference of yaw motion on lateral motion could not be eliminated. This made it impossible to achieve both satisfactory response and convergence. The LQ control system, on the other hand, had a larger number of state feedback coefficients, enabling lateral motion to be separated from yaw motion. This made it possible to set the response and convergence of lateral motion at will. Driving on an automated highway system is premised on the receipt of feedforward information from the road-side infrastructure. In this study, it was shown both theoretically and experimentally that road curvature can be estimated logically as a vehicle travels along even in the absence of feedforward information on curvature. Logical estimates are obtained with an algorithm in which curvature is treated as a state variable. It was also shown experimentally that an autonomous lane-tracking vehicle can even navigate road curves of unknown curvature by using a regulator configured around the method of estimating road curvature logically