Maneuverability Oriented Motion Control Of The Self-balancing Two-wheeled Robots

Recently,smart electric car is common used in some situations including exploration,rescue,transportation and entertainment,the self-balancing two-wheeled robot(TWR)is used as transportation vehicle instead of walking,which is increasingly popular among customers due to its convenient manipulation,high entertaining,and low emission characteristic.TWR is a complicated under-actuated system,which has only two control inputs generated from two DC motors installed on both sides of its body,but with three DOFs,the pitch,the left and right wheel angular velocities of TWR,so it needs high demand for control performance.Nevertheless,accidents caused by TWR occur,and the drivers can easily cause dangerous movements such as the rough road,emergency brake,quick turn and so on,which greatly restricts its extension and application.Therefore,we should design control methods for TWR system to make it stable,safe,and maneuverable.The mathematical model of TWR when it is in the complex road conditions including ramp,uneven road surface and over the step is re-analyzed.TWR system has been divided into two subsystems: longitudinal system and rotational system,then we present a hierarchical fast terminal sliding mode approach to solve the underactuated problem of TWR and the response speed of the system to the equilibrium point is improved.We use Lyapunov control theory to prove the effectiveness of this control method.The motion control system design of TWR based on sliding mode control is completed,and the straight line and steering functions of TWR are realized.Simulation experiments of TWR on different road conditions were carried out on MATLAB/Simulink platform.In the simulation experiment,we prove the hierarchical fast terminal sliding mode approach is helpful to reject disturbances from external environment and reduce shuddering through uneven terrains.The aim is to limit pitch to 0.05 rad range.At the same time,the recovery time of the speed of the emergency brake of TWR is controlled within 2s,at the same time,the shake problem of the pitch when TWR brake is effectively suppressed.We adopt STM32 as the main control board to build a platform of TWR control system to conduct experiments and carry out the whole vehicle motion control experiment.At the same time,the balance car has been modified,we use throttle-steering wheel control strategy to make the balance car can be guaranteed to track the speed at the same time to ensure the balance of body posture and improve its maneuverability.Experimental results show that hierarchical fast terminal sliding mode approach based on model design in this paper achieves the desired effect and completes application in the vehicle.The drivers can move forward,back and turn,and switch speed in the 0.06 rad range on the horizontal road,and drive safely on uneven pavements with shake in the ideal range,which improves the maneuverability of the TWR system from the aspects of safety and comfort.