小麦播种自走式农用移动平台设计与试验

针对农业生产劳动力短缺、人工成本增加和作业效率不高等问题,该研究设计了一种自走式农用移动平台,可更换搭载不同农具进行田间无人驾驶作业,以"机器换人"完成精度高、强度大、重复性强的农业工作。以小麦播种为例,基于全球导航卫星系统(Global Navigation Satellite System, GNSS)定位测速技术、播深控制技术实现自动化播种;采用CAN总线技术、多电机同步驱动技术、差速-电动推杆结合的转向控制方法实现移动平台行走和转向。田间试验结果表明:基于GNSS的电控排种系统稳定可靠,排量稳定性变异系数≤1.8%,播深稳定性系数≥89%.驱动控制系统响应速度快,启动伺服电机2.6 s后实际转速逐渐接近目标转速,同步速度误差变化也趋于相对稳定,平台在负载作业状态下具有较强的抗干扰能力和速度一致性;转向控制系统通过电动推杆驱动车轮转向,转角平均绝对误差0.7°。研究可为促进农业播种智能装备的发展提供参考。

Design and experiment of the self-propelled agricultural mobile platform for wheat seeding

Abstract: Mobile platforms and autonomous vehicles have widely been used for agricultural specific tasks to reduce soil compaction and power consumption, as well as labor saving, compared with traditional large tractors and machinery. In this study, a kind of self-propelled mobile platform was designed for wheat seeding with high precision, high intensity, and strong repeatability in agricultural production. The CAN bus, synchronous multi-motor, and steering control mode were also adopted to implement the movement of mobile chassis in the longitudinal and horizontal directions, concurrently combining differential steering and electromotive push rod. Four control modules of the microcontroller unit (MCU) were designed to realize the communication and motion between platform devices, including serial communication, data acquisition, motion execution, and motor drive module. A four-wheel steering (4WS) fuzzy controller was also proposed using the Ackerman principle and the dynamic model. The total driving power and steering torque of mobile platforms were all evaluated to determine the type selection of servo motor and electromotive push rod. The velocity measurement of the global navigation satellite system (GNSS) and seeding depth control technique were utilized to implement the automatic precision seeding of wheat. The precision seeding was characterized by the use of an electric motor to replace the land wheel. The seeding rate was still controlled when travelling at a non-uniform speed. The travelling speed of the mobile platform was obtained as the input signal, while, the matched motor speed was then settled using GNSS high-precision positioning module. The rotation speed of the seed metering device was constantly readjusted to guarantee the uniformity of seeding. A field experiment was carried out, indicating that the GNSS precision seeding system was stable and reliable. Specifically, the uniform coefficient of variation between rows was not more than 1.8%, and the stability coefficient of seeding depth was not less than 89%. The drive control system presented high response sensitivity. The actual speed gradually approached the target speed after starting the servo motors for 2.6s. The speed synchronization errors tended to be relatively stable, indicating that the mobile platform performed strong anti-interference capability and speed consistency under the condition of loading. The steering control system implemented the wheel deflection, where the bogie frame was driven to rotate through the stroke change of the electromotive push rod. The test results demonstrated that the mean absolute error (MAE) of steering angle was less than 0.7°, indicating that the control accuracy met the expected. This finding can be used to promote the development of intelligent equipment for wheat precision seeding and meet the demand for medium and high-level machinery equipment for agricultural modernization.