Research On Design And Test Of Wheeled AGV System Of Picking Robot Based On Pure-rolling Steering

Picking robot is one kind of agricultural robot and has been widely used.It is a flexible automated mechanical system to complete fruits and vegetables picking,transporting and other tasks.AGV is the guide platform to assist picking robot in conducting field works.Therefore, to ensure picking robot can run smoothly and navigate autonomously,study on AGV system has an important theoretical significance and economic value.This paper selects fruit-vegetable picking robot project as the background, after combining history and present development situation of navigation system and running system for agricultural robot at home and abroad, key problems and solutions of AGV research process are discussed. On the basis of this theory, this paper designs a complete wheeled AGV walking system to assist in completing autonomous picking and transporting tasks of fruit-vegetable picking robot. The main research work of this paper are as follows:First, this paper selects tape guide as the guide way of wheeled AGV after a comparative analysis of various navigation mode. On this basis, the analysis on characteristics of different wheels structure and layout is used to choose two front-wheel steering and two back-wheel differential drive. Aiming at the existence of lateral slippage and tire wear on trapezoidal steering mechanism of wheeled AGV during steering, a pure rolling steering is designed. Using electric putter to change tie rod length of front-wheel steering mechanism in real time to make walking device complies with Ackerman sports model and the turning wheels doing pure rolling movement on the ground.Secondly, this paper builds a wheeled AGV control system, including power module, PLC controller module, drive module, obstacle detection module and magnetic navigation sensor module. Conventional single magnetic guidance techniques cannot measure AGV angle deviation during the process of path tracking,resulting in an uncertainty problem of direction correction and a dual magnetic sensor navigation system is set up. According to the established pure roll steering and differential drive kinematics model and the operating characteristics of magnetic navigation sensor, this paper selects PID control as principle and designs thecorresponding path tracking algorithm. The feedback of current position and angle of deviation as input, the desired front wheel angle and vehicle speed as output. The simulation analysis of algorithm verifies the reasonableness of the magnetic guidance sensor system and the effectiveness of the algorithm design.Finally, this paper debugs the software and hardware after designing programs of wheeled AGV walking system’s function by software FPWIN Rousing prototype to design pure rolling steering, differential drive, minimum turning radius and circular curve path tracking experiment. The results show that the maximum error of instantaneous center point set over PP’ is 5.17 mm, no jitter and noise caused by lateral friction and it steering smoothly when moving; the direction of rectification is determined accurately during circular curve path tracking process and the maximum error between actual running and preset trajectory is 0.009 m, the error is less than1 cm and the effect of path tracking is good.