Smooth Trajectory Tracking Using Longitudinal Distance Constraint for A 4WS4WD Unmanned Ground Vehicle The modelbased trajectory tracking method of four wheel steering and four wheel drive (4WS4WD) unmanned ground vehicles (UGVs) needs to establish accurate vehicle kinematics and dynamics models, which is computationally complex thus functioning poorly in realworld scenarios. The geometrybased method, i.e., the pure pursuit method, uses the position information to regulate vehicleu0027s steering angle, which has good realtime performance in practical applications. However, the existing pure pursuit method only considers the lookahead distance constraint, ignoring the influence of the longitudinal distance which affects the smoothness of the vehicle trajectory. It may cause the vehicle to oscillate back and forth around the target trajectory. This work proposes an improved pure pursuit method with longitudinal distance constraint (LDC) to avoid the vehicle oscillation effectively. Additionally, to alleviate the cornering cutting problem, a fuzzy logic based controller is proposed to dynamically adjust the lookahead distance according to the curvature. A comparative experiment between the proposed method and the conventional pure pursuit method was conducted. Results show that the proposed method has better trajectory smoothness and tracking accuracy than the traditional pure pursuit method.

Model Predictive Control based Dynamic Path Tracking of a FourWheel Steering Mobile Robot This paper develops a new constrained model predictive control for a dynamic path tracking of an offroad mobile robot with a double steering axle. The controller is based on a dynamic model that includes wheelground lateral slippage and terrain geometry parameters. It is formulated as an optimization problem that computes at each timestep the optimal front and rear steering angles required to perform a desired path, with respect to multiple constraints, essentially the steering joint limits and the tire adhesion area bounds (i.e., pseudosliding zone limits). The capabilities of such a path tracking controller are shown and discussed through numerical simulations and experiments on a real offroad mobile robot at different speeds.