基于前馈模型预测控制的类车机器人路径跟踪

Path tracking of car-like robots based on feed-forward model predictive control

  • 摘要: 在类车机器人路径跟踪控制方法中,模型预测控制(Model predictive control, MPC)在处理系统约束方面具有较大优势,但是现有的非线性模型预测控制(Nonlinear MPC, NMPC)实时性较差,线性模型预测控制(Linear MPC, LMPC)精确性较差,因此亟需提出一种同时具有较高精确性与实时性的类车机器人路径跟踪控制方法. 为此,以无预瞄点的LMPC为基础,引入基于逆运动学模型的前馈转向角信息,提出了一种前馈模型预测控制(Feedforward MPC, FMPC)方法,并通过MATLAB和Carsim进行了联合仿真测试. FMPC具有较高的精确性,在所有仿真结果中,位移误差绝对值不超过0.1110 m,航向误差绝对值不超过0.1177 rad. 在相同工况下,FMPC与NMPC精确性相当,LMPC、前馈控制和Stanley控制误差发散. FMPC也具有较高的实时性,在每个控制周期内的解算时间不超过4.31 ms. 在相同工况下,FMPC与LMPC实时性相当,相比NMPC能将每个控制周期内解算时间的最大值减小80.68%,平均值减小65.14%. 此外,FMPC能够保证控制变量在系统约束范围内,且受定位误差的影响较小.

     

    Abstract: Car-like robots are mobile robots commonly used in manufacturing and warehousing. This type of robot has a mechanical structure similar to that of an unmanned vehicle, which uses the front wheels as steering structures. However, this type of robot has characteristics that significantly influence path tracking control relative to unmanned vehicles, such as a larger magnitude of reference path curvature, a smaller range of system constraints, and a lower degree of part standardization. Consequently, several research efforts dedicated to path tracking for car-like robots have emerged. Among the path-tracking control methods for car-like robots, model predictive control (MPC) has a tremendous advantage in dealing with system constraints. However, the existing nonlinear model predictive control (Nonlinear MPC, NMPC) has inferior real-time performance, and the linear model predictive control (LMPC) has poor accuracy. Therefore, a path-tracking control method for car-like robots with high accuracy and superior real-time performance needs to be developed. Because the reason for the low accuracy of LMPC in paths with significant curvature changes is that the response of LMPC is not timely after the curvature change, the idea of combining LMPC and feed-forward information is adopted. The basis of path-tracking controller for car-like robots is the LMPC. The reference front wheel angle at the reference path point in front of the car-like robot is obtained as a feed-forward signal through an inverse kinematic model. A feed-forward optimization objective function that conforms to the LMPC architecture is designed, and a feed-forward model predictive control (FMPC) is proposed by combining the feed-forward optimization objective function with the LMPC. The FMPC is tested by joint simulation using MATLAB and CarSim. The FMPC has high accuracy, the absolute value of the displacement error in all of the simulation results does not exceed 0.1110 m, and the absolute value of the heading error does not exceed 0.1177 rad. The accuracy of the FMPC is comparable to that of the NMPC under the same conditions, and the errors of LMPC, feed-forward control, and Stanley control are dispersed under these conditions. The FMPC also has superior real-time performance, and the solving time in each control period does not exceed 4.31 ms. Under the same conditions, the FMPC is comparable to the LMPC in terms of real-time performance and can reduce the maximum value of the solving time in each control cycle by 80.68% and the average value by 65.14% compared with the NMPC. The FMPC can also ensure that the control variables are within the system constraints and are less affected by positioning errors.

     

/

返回文章
返回