基于稳定性评价的无人矿卡轨迹跟踪无模型自适应控制方法

Stability-based model free adaptive control method for trajectory tracking of unmanned mining trucks

  • 摘要: 在无人矿用卡车的轨迹跟踪任务中,露天矿的地形信息繁杂且路面类型多样,导致跟踪精度与横向稳定性之间的矛盾突出;此外,无人矿卡轮地交互的动力学特性复杂,矿卡的轨迹跟踪面临建模难度大的挑战。针对以上问题,提出了一种基于稳定性评价的无模型自适应控制(Stability-based Model Free Adaptive Control,SMFAC)方法,以数据驱动的方式实现对行驶稳定性和跟踪精确性的协调控制。在Pacejka轮胎公式的基础上引入路面附着系数对矿卡的影响,结合简化的动力学方程构建矿卡的质心侧偏角−质心侧偏角速度相平面,并对不同环境工况的稳定域边界实现动态辨识,实时求解矿卡的稳定系数。基于径向基网络构建Actor-Critic无模型轨迹跟踪控制器,Actor网络依据系统状态计算控制量,Critic网络评估实时控制量的价值并对价值函数进行拟合;结合稳定系数设计学习过程中的网络误差,以最小化误差函数为目标求解隐藏层权值的更新律,通过矿卡与环境的交互迭代出轨迹跟踪的最优策略。基于CarSim与MATLAB/Simulink搭建轨迹跟踪联合仿真系统,以验证所提出的SMFAC方法的有效性。结果表明:相比于无模型的PID算法与有模型的MPC与LQR算法,所提方法在低速与高速的情况下均可兼顾角度跟踪精度与横向跟踪精度,在双移线、单移线、曲线工况中均取得最优轨迹跟踪性能。此外,SMFAC方法可抑制输出动作的波动,生成较为平滑的行驶轨迹,保障了无人矿卡的操纵稳定性。

     

    Abstract: In the trajectory tracking task of autonomous mining trucks, the terrain information in open-pit mines is intricate and the road surface types are diverse, resulting in a pronounced conflict between tracking accuracy and lateral stability. Furthermore, the dynamic characteristics of the tire-ground interaction in autonomous trucks are complex, presenting significant challenges in modeling for trajectory tracking. To address the above issues, a Stability-based Model Free Adaptive Control (SMFAC) method is proposed, which achieves coordinated control of driving stability and tracking accuracy in a data-driven manner. Based on Pacejka tire model, the influence of road friction coefficient on the system is introduced. The centroid side slip angle versus centroid side slip angle velocity phase plane of mining trucks is constructed by the simplified dynamic equation. The boundary of stability region under different environmental conditions is identified dynamically to solve the stability coefficient. In addition, an Actor-Critic framework is constructed using radial basis function networks for the model-free trajectory tracking controller. The Actor network calculates the control quantity based on the system state, while the Critic network evaluates the value of the real-time control quantity and fits the value function. The stability coefficient is employed to design the network error during the learning process, aiming to minimize the error function to update weights of the hidden layer. By iteratively interacting with the environment through the mining truck, an optimal strategy for trajectory tracking is developed. A trajectory tracking simulation system is built on the CarSim and MATLAB/Simulink integrated platform to validate the effectiveness of proposed method. The results indicate that, compared with the model free PID algorithm and the model-based MPC and LQR algorithms, the proposed method can take into account both the angle tracking accuracy and the lateral tracking accuracy at both low and high speeds. And proposed method achieves the optimal trajectory tracking performance in double lane shift, single lane shift, and curve conditions. In addition, the SMFAC method can suppress the fluctuation of the output action, generate a smoother driving trajectory, and ensure the control stability of the unmanned mining truck.

     

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