Tracking Control of a Four-Wheeled Skid-Steered Robot with Slip Compensation and Application of the Drive Unit Model

This article focuses on trajectory tracking control of a four-wheeled mobile robot, with non-steered wheels. The issues in terms of robot kinematics are discussed and a dynamics model is derived, which additionally took into account the drive unit model. This paper analyses four versions of the control system, which take into account the possibility of compensating for wheel slip and non-linearities resulting from the drive unit model. It is assumed that the wheel-slip compensation is based on the measurement of the actual robot’s motion parameters. The linear and angular motion parameters of the robot’s mobile platform are taken into account, which allows for the estimation of the wheel slip velocities. The results of the simulation studies are presented, consisting of the evaluation of individual control system solutions in terms of achieving the highest possible accuracy in executing a prescribed trajectory. Additionally, the impact of the investigated control strategies on electric power demand and electric energy consumption by the robot’s drives is analyzed. In order to quantitatively assess the control system solutions, quality indexes were adopted, focusing on tracking accuracy and energy efficiency. The research results indicate that incorporating wheel-slip compensation into the control system enables high accuracy to be achieved in terms of trajectory tracking. In turn, the use of the drive unit model within the control system leads to an increase in the accuracy of the robot’s wheel movements, which does not ultimately result in an increase in the accuracy of the motion of the robot’s mobile platform due to the slipping of the wheels. It was also observed that improving the trajectory tracking accuracy leads to an increase in the maximum electric power demand and electric energy consumption by the robot’s drives.