Solving practical problems in Hilare-type mobile robot trajectory tracking control via application of nonlinear model predictive control

This research work is focused on solving the practical problems that arise in trajectory tracking control of Hilare-type robot, using the advantages of the Nonlinear Model Predictive Control (NMPC) Method. The saturation of control inputs causes a practical problem in controlling a Hilare-type robot on 2D surfaces, when the conventional controller is employed. A conventional controller is developed based on the kinematic model of the Hilare-type robot, which is considered to be situated on a 2D surface. The left and the right wheel velocities of the robot are considered as the control inputs and are limited to certain allowable limit, which cause inputs saturation if the robot comes up with a wheel velocity greater than this optimum level. The failure of the conventional controller when the control inputs are saturated is confirmed through simulation and experimentation results. This problem can be accomplished using NMPC method, because NMPC has the capacity to assimilate constraints in the control law. The maximum allowable wheel velocities of the robot are given as the constraints on the control inputs generation. The NMPC controller is synthesized based on the kinematic model of the Hilare-type robot in 2D. The simulation and experimentation results exhibit that the problem that causes due to input saturation in trajectory tracking control of a Hilare-type robot is solved.;The conventional controllers have shortcomings for controlling Hilare-type robots on slippery 3D terrains. The highly satisfactory performance of the proposed control method is encouraged to go for dynamic control of Hilare-type robots on slippery 3D terrains, while preventing wheel slip. The dynamics of the Hilare-type robot are deduced by considering 3D pose of the robot, which is situated on top of a hill. So, the dynamic equations and the control law consist of roll and pitch angles, representing the slope of the terrain. These Euler angles are feedback to the system in real-time to attain more reliable controller performance. The maximum affordable longitudinal and lateral static friction forces are given as the constraints on control inputs production. The Hilare-type robot is simulated while tracking a straight path on a terrain of known static friction. The results from the simulation bespeak that the designed controller is successful in allowing the Hilare-type robot to track the desired trajectory on the slippery hill of known static friction, without wheel slip.