考虑滑移滑转的双电机履带底盘路径跟踪算法

    Path tracking algorithm of the dual motor tracked chassis considering skid and slip

    • 摘要: 针对履带底盘田间作业时由于土壤松软、田面不平整导致履带滑移滑转、自动导航路径跟踪精度低的问题,该研究提出了考虑滑移滑转的履带底盘路径跟踪算法,基于履带底盘运动学模型推导出表征滑移滑转特性的转向半径修正系数,并设计了一种基于预瞄模型的模糊控制路径跟踪算法。该方法在纯模糊控制基础上通过预瞄模型确定预瞄点,进而得到横向偏差与航向偏差,同时在常规模糊控制器中引入转向半径修正系数,建立横向偏差、航向偏差、转向半径修正系数三输入模糊控制器。以双电机履带底盘为控制对象,采用高精度RTK-GNSS和MTi-30惯性传感器获取底盘实时位姿信息与角速度信息,进行组合导航。开展了三输入模糊控制器田间U型路径跟踪试验,结果表明,三输入模糊控制器的直线跟踪最大绝对偏差、平均绝对偏差和标准差分别为12.0、3.6和4.4 cm;三输入模糊控制的曲线跟踪最大绝对偏差、平均绝对偏差和标准差分别为21.3、8.6和8.4 cm;为进一步确定本研究算法在履带出现滑移滑转时对路径跟踪精度的提升效果,开展了常规模糊控制器与三输入模糊控制器曲线路径跟踪对比试验,结果表明:当作业速度为0.6 m/s时,常规模糊控制器的最大绝对偏差、平均绝对偏差和标准差分别为31.1、8.3和10.2 cm,三输入模糊控制器的最大绝对偏差、平均绝对偏差和标准差分别为22.4、7.4和9.1 cm,相较于常规模糊控制器,路径跟踪精度分别提高了27.95%、10.84%和10.78%,所设计的三输入模糊控制器可有效降低履带滑移滑转的影响,增强导航系统的控制性能,可为履带底盘在田间松软土壤环境下高精度导航作业提供参考。

       

      Abstract: Track skid and slip often occur, when the tracking chassis work in soft soil and uneven field. The accuracy of curved path tracking can inevitably deteriorate in automatic navigation. In this work, path tracking was designed to consider the track skid and slip in field conditions. Firstly, the coefficient of turning radius correction was derived to describe the skid and slip characteristics using the kinematic model of the tracked chassis. Then, the lateral and heading deviations were determined by the look-ahead model. Finally, a three-input fuzzy controller was established with the controller inputs of lateral deviation, heading deviation and turning radius correction coefficient. A dual-motor tracked chassis was designed to validate the model. The control hardware included two brushless DC motors, a motor driver, an STM32 microcontroller, and two photoelectric rotary encoders. In navigation, the position, heading and angular velocity of the chassis were measured by a high-precision RTK-GNSS and an MTi-30 inertial sensor. The measurement values were sent to the upper-level computer using a serial port. The path tracking was carried out to calculate the control signal, and then sent into the lower-level microcontroller. The tracking of the reference path was realized by the motor driver of the lower-level microcontroller on both sides. A field experiment was conducted on automatic navigation to verify the performance of a three-input fuzzy controller. The field was selected with a lot of weeds, where the soil was wet and sticky with a moisture content of 22.4%. There was the low flatness with some pits, bulges and hardened soil blocks that scattered throughout the whole field. The speed of the chassis was set to 0.6 m/s in navigation. The look-ahead distance proportional coefficient of the look-ahead model was set to 1.5. An initial lateral deviation of about 1000 cm was set for the correction. The results showed that the average response time of the control system was 6.79 s, while the average distance was 4.08 m. The tracking test of the U-shaped path was performed on the three-input fuzzy controller. The maximum absolute deviation, average absolute deviation and standard deviation of the straight-line and curve tracking section were 12.0 and 21.3 cm, 3.6 and 8.6 cm, as well as 4.4 and 8.4 cm, respectively. The curve tracking with the three-input fuzzy controller was compared with the conventional one, in order to further determine the path tracking accuracy under track skid and slip. The maximum absolute deviation, average absolute deviation and standard deviation of the conventional and three-input fuzzy controller were 31.1 and 22.4 cm, 8.3 and 7.4 cm, as well as 10.2 and 9.1 cm, respectively. Compared with the conventional, the three-input fuzzy controller was improved by 27.95%, 10.84 % and 10.78 %, respectively, in the maximum absolute deviation, average absolute deviation and standard deviation. The better control performance of the navigation system was achieved in the three-input fuzzy controller, indicating the reduced influence of track skid and slip. This finding can also provide a strong reference for the high-precision navigation of tracked chassis in soft soil environments in the field.

       

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