Since the interest to unmanned ground vehicles is increasing worldwide, a lot of studies on commercial UGV(Unmanned Ground Vehicle) has been carried out by many researchers. There have been a lot of studies which deal with the control of an UGV when the desired trajectory and velocity are given. The study on the calculation of maximum allowable driving velocity, however, seems rare to be found from the literatures. In this study, an UGV which will be used for military purpose to traverse on off-road terrain is studied to decide the maximum allowable driving velocity while keeping its stability.
To get the maximum allowable velocity, this study requires real-time parallel driving simulations. Since the driving simulation for about 15 m ahead should be finished within 100 msec, it is required to have an efficient vehicle dynamics model for real-time simulation. Given a tracking path, the parallel simulation is carried out using 7 kinds of constant velocity candidates. On each driving simulation, the path tracking control which comprises preview distance concept, disturbance moment observer and in-wheel motor torque distribution is used so that the vehicle can drive along with the designated driving velocity candidate in the given path.
The vehicle stability analysis is carried out at every driving simulation step to find the maximum allowable driving velocity. The vehicle stability indices consist of roll stability, pitch stability, lateral stability and vertical acceleration stability. All of those 4 kinds of stability indices must be satisfied to qualify the desired velocity on each waypoint. The results of stability indices are used to calculate the maximum allowable velocity profile over the entire driving path. The vehicle’s maximum acceleration and deceleration capability should also be considered to have optimal velocity profile so that the vehicle’s velocity profile become realistic.
In the last stage of the study, a verification of optimal velocity profile is also carried out to make sure that the velocity profile guarantees the vehicle’s stability.