Implementation Of Double Closed-Loop Control System For Unmanned Ground Vehicles

Abstract The research work focuses on issues of vehicle modeling incorporating wheel-terrain interaction and low-level control design taking into account uncertainties and input time delay. Addressing these issues is of significant importance in achieving persistent autonomy for outdoor UGVs especially when navigating on unprepared terrains. The vehicle is driven in the skid-steering mode which is popular for many off-road land vehicle platforms. In this research work a comprehensive approach is proposed for modeling the dynamics of UGV. The approach considers the difference in speed between two outputs of the differential and the turning mechanism of the vehicle. It describes dynamics of all components in the vehicle driveline in an integrated manner with the vehicle motion. Given a pattern of the throttle position left and right braking efforts as the inputs the dynamic behavior of the wheels and other components of the UGV can be predicted. For controlling the vehicle at the low level PID controllers are firstly used for all actuators. As many components of the vehicle exhibit nonlinearities and time delay the large overshoots encountered in the outputs can lead to undesirable vehicle behaviors. To alleviate the problem a novel control approach is proposed for suppression of overshoots resulting from PID control. As a result the proposed approach can improve significantly system robustness and reduce substantially step response overshoot. Notably the design is generic in that it can be applied for many dynamic processes. Knowledge of the interaction between the UGV and the terrain plays an important role in increasing its autonomy and securing the safety for off-road locomotion. The novel interaction model takes into account the relationship between normal stresses shear stresses and shear displacement of the terrain that is in contact with the wheels in deriving the three-dimensional reaction forces. Finally all modeling and control algorithms are integrated into a unique simulator for emulating the vehicle mobility characteristics. In particular the wheels slip and rolling resistance can also be derived to provide useful information for closed-loop control when the UGV is navigating in an unknown environment.