| Two-wheeled self-balancing vehicles(TWSBVs)have important values in numerous fields,such as transportation,warehouse logistics and home service,owing to their compact construction,high maneuverability,and low energy consumption,etc..Trajectory planning and tracking control are key techniques of the motion control for TWSBVs,which is the foundation of their efficient autonomous motion and performing related tasks.However,this kind of vehicle has typical nonholonomic and underactuated characteristics,and confronts multi-constraints of internal stability and external obstacle avoidance,which make the trajectory planning and tracking control quite challenging.To this end,this dissertation fully considers the vehicle’s kinematic and dynamical characteristics,as well as the multi-constraints on the planning level,thus the difficulty of the tracking controller design can be reduced significantly.Meanwhile,the motion control performance and the ability to adapt to multi-obstacle environments can be improved.The main research works are as follows:Firstly,aiming at the point stabilization problem of TWSBVs,the trajectory planning method under internal stability constraints of velocity,acceleration,and tilt angle of the vehicle body,etc.is studied.To avoid the barrier introduced by the nonholonomic characteristic,the point stabilization is achieved by performing pivot steering and longitudinal motion successively.And a kinematic coupling-based longitudinal trajectory planning approach is presented to solve the underactuated problem,thus the asymptotically stable point stabilization can be implemented.Furthermore,to realize the time-optimal point stabilization,the optimal trajectory planning can be transformed to a quasi-convex optimization problem,which can be solved by a bisection method to obtain the discrete optimal trajectory.And a B-spline adaptive interpolation algorithm is proposed to acquire the optimal trajectory with an analytical expression.Then,a normal tracking controller is designed to track the planned trajectory,and the desired point stabilization can be realized.Secondly,considering the obstacle avoidance problem of TWSBVs,the trajectory planning and coordinated control strategy under external environmental constraints of motion space and obstacles is studied.For the annular motion space,a circular and uniform trajectory is selected as the planned trajectory,and a coordinated control strategy based on the non-singular terminal sliding mode control and the linear quadratic regulator is adopted to track the planned trajectory.In this way,the vehicle’s obstacle avoidance under motion space constraint can be implemented.Aiming at the road obstacle environment,a smooth obstacle avoidance trajectory planning method based on circular arcs and transition curves is proposed,and the trajectory with continuous curvature and approximately zero longitudinal acceleration can be obtained.On this basis,a stable tracking control strategy based on direct adaptive fuzzy and nested saturation approaches is constructed to ensure the trajectory tracking even with the bigger initial tilt angle and external disturbance.Thirdly,aiming at the efficient motion control problem of TWSBVs in multi-obstacle environments,the optimal trajectory planning method considering both internal stability and external obstacle avoidance is studied.For the mixed obstacle environment,an improved artificial potential field is deduced with the safe distance being introduced,and a real-time planning and tracking controller is designed for obstacle avoidance based on the improved artificial potential field.In addition,the key parameter in the controller is adjusted by fuzzy logic to stablilize the system and improve the efficiency of obstacle avoidance.Furthermore,considering the unknown obstacle environment and optimal motion target,a multi-object optimized path solution algorithm based on the self-building map is developed.Thereafter,combining the internal stability constraints,a minimum-time trajectory planning method along the optimized path is proposed.On that basis,a tracking controller is designed to track the planned trajectory,and the optimal motion in unknown obstacle environment under internal and external constraints can be realized.Finally,the experimental systems of TWSBVs are built based on the ultra-wide band(UWB)location technique and robot operating system(ROS)to verify the related theoretical methods.A trajectory planning and tracking control experimental system is built based on the UWB location technique with single chip and inertial measurement unit,and experiments of the trajectory planning method for the point stabilization under internal stability constraints and the trajectory planning and coordinated control strategy aiming at external obstacle avoidance are both conducted.In addition,the experimental system for environmental map building and navigation control is designed based on ROS with Raspberry Pi single board computer and laser radar,etc.,and the experiment for the optimal trajectory planning method considering internal stability and external obstacle avoidance is performed.Experimental results show that the desired motion control effects can be achieved based on the built experimental platforms and related theoretical methods. |
