装载机避障轨迹规划及模型预测轨迹跟踪

轮式装载机在工作区域行驶时，避障过程频繁，以往的避障轨迹规划未考虑整车转向半径约束和车速变化，也较少考虑整车在动力学模型条件下的轨迹跟踪性能。针对上述情况，以自动驾驶轮式装载机为对象，基于最优快速随机扩展树算法（RRT^*），考虑车身膨胀圆个数，生成全局最优避障路径，以整车最小稳定转向半径为约束，利用CC-Steer算法对避障路径进行平滑处理，采用路径-速度分解算法规划满足整车在加速、匀速和减速状态下的避障行驶轨迹。基于整车动力学模型，考虑行驶过程中的横向位置偏差和航向角偏差，并将整车动力传动系统视为1阶惯性环节，构建装载机动力学状态空间方程。以加速度和铰接角为控制输入，以车速、横向位置偏差和航向角偏差为控制输出，建立整车动力学预测模型，以加速度、铰接角和车速为约束条件，将目标函数转换为二次规划问题，建立满足装载机在工作区域避障的模型预测轨迹跟踪控制系统。以规划的非匀速行驶避障轨迹为目标，利用构建的模型预测轨迹跟踪系统，进行自动驾驶轮式装载机的轨迹跟踪仿真。研究结果表明：所提方法能够很好地控制自动驾驶轮式装载机从初始位姿驶向目标位姿，实现整车在工作区域的避障过程，且在避障过程中满足整车的约束要求，保证整车在轨迹跟踪过程中的安全稳定性能。

Obstacle Avoidance Trajectory Planning and Model-predicted Trajectory Tracking of Wheel Loaders

To address the problem of poor trajectory planning and tracking during obstacle avoidance for wheel loaders, a trajectory-planning method considering the constraints of the turning radius and dynamic change in vehicle speed was proposed. A model-predictive trajectory-tracking system for the entire vehicle based on the dynamic model of the wheel loader was constructed. In this method, based on the optimal rapidly exploring random tree algorithm and considering the number of inflation circles in the automobile body based on collision risk, the global optimal obstacle avoidance path was generated for the automobile wheel loader. By considering the minimum stable steering radius of the vehicle as a constraint, the path for obstacle avoidance was smoothed using the continuous curvature steer algorithm, and the path-velocity decomposition algorithm was adopted to plan the obstacle avoidance trajectory of the vehicle under the condition of variable-speed driving. Based on the dynamic model of the wheel loader and considering the lateral deviation and relative yaw angle in the course of driving, the vehicle powertrain was regarded as the first-order inertia link, and the vehicle dynamics prediction model was established based on model-predictive control. The objective function was converted into a quadratic programming problem by considering the acceleration, articulation angle, and vehicle speed as constraints, and a model-predictive trajectory-tracking control system was established to satisfy the obstacle avoidance of wheel loaders in the working area. Based on the obstacle avoidance trajectory generated by the planning, the model predictive trajectory-tracking control system was used to perform obstacle avoidance simulation. The results demonstrate that the constructed system can control the autonomous wheel loader from the initial position to the target position, realize the obstacle avoidance process of the vehicle in the working area, and meet the constraints of the vehicle to ensure the safety and stability of the vehicle during trajectory tracking.