基于虚拟探照灯的离合制动履带底盘寻径跟踪

Path finding and tracking of clutch brake track chassis based on virtual searchlight

油动履带底盘由于具有成本低、技术成熟、动力充足、续航能力强、维修便捷等特点而被广泛应用于农业生产,但其操控精度低、振动严重等问题对其应用造成挑战。该研究以农用油动履带底盘为对象,根据共性传动结构提出离合制动式履带底盘,并以STM32F303作为主控器搭建基于实时动态差分全球导航卫星系统(real-time kinematic global navigation satellite system,RTK-GNSS)的自动导航系统,建立其运动学模型,提出一种改进模糊式预瞄控制算法—虚拟探照灯寻径跟踪(virtual searchlight pathfinding tracking,VSPT)算法。针对横向偏差和速度变化引起的跟踪振荡问题,提出基于横向偏差指数的视域角动态调整方法和基于行驶速度的虚拟目标点判断方法,并通过仿真和试验验证算法的有效性。仿真结果表明,在底盘前进速度0.4 m/s时,横向偏差指数λ、视域增益k1和目标增益k2取值分别为1/4,0.005 rad·m和6 s^(-1)时可获得较好的导航效果。现场试验结果表明,在水泥路面,不同初始位姿下,直线导航平均上线距离为1.64 m,平均横向偏差和航向偏差为0.44 cm和1.57°;行驶速度提高会导致导航精度降低,适当修正k1、k2可维持较好的导航效果,3种行驶速度下获得的平均横向和航向偏差分别为0.75 cm和1.05°,平均纠偏次数为4.7次;田间路况下,由于土路附着系数增加,转向相对平稳,纠偏次数降低至2.7次,相同参数时2种路况下的导航效果接近。研究表明,VSPT算法针对离合制动式履带底盘具有良好的跟踪效果和路况适应性,该研究可为离合制动履带平台提供一种高效、稳定的导航控制方案。

Chassis assembly is one of the core components in mobile agricultural power machinery.A universal chassis can carry the functional tools to realize the various activities in agricultural production.Among them,the oil-operated track chassis are widely used in recent years,due to their low cost,mature technology,sufficient power,high range,and easy maintenance.But their low handling accuracy and severe vibration have posed great challenges to the application of automatic navigation.In this study,the concept of clutch-braked track chassis was proposed as a low-cost agricultural oil-operated track chassis platform.Stronger traction was achieved during steering,compared with differential track chassis vehicles.The RTK-GNSS-based automatic navigation system was built with the STM32F303 as the main controller.The working path of agricultural machines generally consisted of a straight line in the actual operation.The process of tracking was divided into the desired path of the track chassis platform online and the straight line tracking,according to the online point(the online point referred to the sampling point with a lateral deviation less than 3.0 cm,heading deviation less than 2.0°,and the closest distance to the starting position).The kinematics model was established using the transmission and motion of the platform vehicle.A virtual search light pathfinding tracking(VSPT)was proposed to represent the pseudo-code of the VSPT.The fuzzy pre-scanning control was enhanced to search for the target points within the searchlight's field of view in real time.The steering of the track vehicle was controlled to expose the target points within the field of view at all times.In addition,the field of view angle was dynamically adjusted for the tracking oscillation caused by the lateral deviation and speed change.The lateral deviation index and a virtual target point judgment were utilized with a positive proportional relationship of speed.The logical process was designed for the data flow diagram.Direct memory access(DMA)data transfer was used with the idle interrupt and cyclic mode to complete the reception of variable-length byte data.The operation efficiency of the single-chip computer was improved to design the logic flow for the data flow diagram.The improved model was verified to calibrate the relevant parameters by simulation tests.The better navigation was achieved at the chassis forward speed of 0.4 m/s,where the parameters lateral deviation indexλ,field-of-view gain k1,and target gain k2 were taken as 1/4,0.005 rad∙m and 6.0 s^(-1),respectively.Subsequently,the calibrated parameters after simulation were used for the field tests.The results showed that:the average online distance was 1.64 m,while the average lateral and heading deviations were 0.44 cm and 1.57°,respectively,for 6 different initial positions under concrete road conditions.The navigation tests showed that the increasing speed led to a decrease in the navigation accuracy.The appropriate correction of parameters was conducted to maintain better navigation.The average lateral and heading deviations were 0.75 cm and 1.05°,respectively,under 3 speeds,where the average number of corrected deviations was 4.7 times.The number of corrected and heading deviations were reduced under the field dirt road conditions,due to the increasing adhesion coefficient of the dirt road and relatively smooth steering.But the navigation effect was similar under the same parameters in both road conditions.Therefore,the VSPT performed better tracking and adaptability for the control of the clutch-braked track platform.This finding can provide an efficient and stable control scheme for the clutch-braked crawler platforms with navigation algorithms.