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.