矿山无人驾驶铰接车辆纯追踪算法参考点选取及误差分析

Reference point selection and error analysis of pure pursuit algorithms for autonomous mining articulated vehicles

  • 摘要: 纯追踪模型凭借结构简洁、强实时性和工程易实现性,成为低速无人驾驶车辆路径跟踪的核心算法之一,在阿克曼转向车辆中已得到有效验证。区别于传统刚性车体,铰接车辆由前后车体通过铰接机构连接构成,当选择前轴中心或后轴中心作为参考点(PPF或PPR)时,转向控制量生成机制存在差异,直接影响路径跟踪效果。基于纯追踪算法构建折腰转向铰接车辆的转向目标计算模型,重点探讨参考点选取对控制精度的影响机制,同时引入载荷分布量化参考点选择的敏感度。通过Gazebo平台建立铰接矿车三维模型,在ROS框架内集成激光雷达SLAM系统,规划U型测试路径并优化前视距离参数。在空载、半载及满载工况下,分别对比PPF与PPR的跟踪性能。实验表明:在U型弯道跟踪中,3种载荷下,PPF产生的最大横向误差和最大航向误差均小于PPR。相比于PPR,空载时PPF的最大横向误差降低25.32%~25.78%,最大航向误差减少31.42%;半载时PPF的最大横向误差降低24.59%~24.66%,最大航向误差减少31.06%~31.37%;满载时PPF的最大横向误差降低22.37%,最大航向误差减少30.00%~32.00%。同时,随着前车体装载质量的增加,PPF与PPR的跟踪误差呈现下降趋势,且最大横向误差降低3.85%~8.07%,最大航向误差减小2.77%~5.55%,然而,因装载质量增加所带来的误差减小程度明显低于参考点位置参数改变所引起的误差变化,由此表明,相较于载荷分布状态,路径跟踪误差对参考点位置参数更为敏感。

     

    Abstract: The pure pursuit model has become one of the core algorithms for path tracking of low-speed autonomous vehicles by virtue of its simplicity of structure, strong real-time performance, and engineering ease of implementation, and has been effectively validated in Ackermann steering vehicles. Different from the traditional rigid body, the articulated vehicle consists of the front and rear bodies connected by an articulation mechanism, and when choosing the front axle center or the rear axle center as the reference point (PPF or PPR), there are differences in the steering control volume generation mechanism, which directly affects the path tracking effect. The steering target computational model of a folded-waist steering articulated vehicle is constructed based on the pure pursuit algorithm, focusing on the mechanism of the influence of the reference point selection on the control accuracy, and at the same time, the load distribution is introduced to quantify the sensitivity of the reference point selection. A 3D model of articulated mining vehicle is built by Gazebo platform, and a LiDAR SLAM system is integrated within the ROS framework to plan the U-shaped test path and optimise the forward-looking distance parameters. The tracking performance of PPF and PPR is compared under no-load, half-load and full-load conditions, respectively. The experiments show that in U-turn tracking, the maximum lateral error and maximum heading error generated by PPF are smaller than those of PPR under all three loads, and compared with PPR, the maximum lateral error of PPF is reduced by 25.32%‒25.78% and the maximum heading error is reduced by 31.42% when no-load, and the maximum lateral error of PPF is reduced by 24.59%‒24.66% when half-load, and the maximum heading error is reduced by 31.06%‒31.37%; the maximum lateral error of PPF at full load is reduced by 22.37% and the maximum heading error is reduced by 30%‒32%. Meanwhile, as the loading mass of the front body increases, the tracking errors of PPF and PPR show a decreasing trend, and the maximum lateral error decreases by 3.85%‒8.07%, and the maximum heading error decreases by 2.77%‒5.55%. However, the degree of error reduction resulting from the increase in loading mass is significantly lower than the error variation caused by the change in reference point position parameters. This indicates that, compared with the load distribution state, path - tracking errors are more sensitive to reference point position parameters.

     

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