Study On Automatic Turning Path And Actuator Of Agricultural Tractor

Tractors are the main agricultural in the field operation.Its unmanned technology is a hot spot of research.Among them,the automatic driving path planning of the tractor has an important influence on the quality and efficiency of the operation,and is the focus of the study.At present,there are still deficiencies in the automatic turning technology of the unmanned tractors in field trials.It still needs people to carry on the steering operation,and people should also be on the tractor in the straight line,so that the manual and automatic driving will be switched when the tractor needs to turn at the edge of the field,and the turning and changing are done by human operation.The research on the path planning algorithm and executive mechanism for automatic turning of tractors at the edge of the field can provide the design basis for automatic steering,so as to improve the automation and intelligence of the field work,further improve the precision of field work and reduce the labor intensity.This paper analyzes the turning principle and turning strategy of agricultural tractors,a turning strategy was put forward with considering the turning radius of the tractor,the width of the operation and the turning space of the head.That is to complete the turn of the designated target after many advances and backwards.The agricultural tractor was simplified as a rectangular model with Ackerman steering principle.Without neglecting the size of the body structure,aiming at the tractor with front wheel steering and rear wheel steering,the turning kinematic model was established based on the center point of rear axle and the center point of front axle.According to the turning strategy and kinematic model of agricultural tractors and the requirements for the goal to complete the U-turn in the limited space.Taking alternate times and operation width errors as the judging conditions for finding the best path,the turning path algorithm of agricultural tractors was designed by using MATLAB.It includes search,forward and backward computation,optimization and trajectory generation.The MATLAB software is used to simulate the turning path planning algorithm.The results show that the optimal turning path can be found for different operation conditions.The algorithm can provide a design basis for the automatic turning path planning of unmanned agricultural tractors.In order to intuitively output operation results of algorithm program,the turning path optimization interface was designed by using GUI module of MATLAB.In order to turn according to the planning path.On the basis of the study of the original steering system and the present automatic steering actuators of B-1104,two design schemes of automatic steering actuators were proposed.Through the analysis,the scheme of the parallel hydraulic steering gear was selected.Through the analysis of PID control,proportional control and PD control,PD control was selected as the control method of automatic steering.And the simulation analysis was carried out.The results show that PD control can be faster to achieve stability and the overshoot is small.In order to facilitate the turning of the tractor and reduce the turning range,a steering device was designed to achieve the original steering.The structure was determined by calculation and stress analysis.The kinematic analysis of the lifting and turning motion was carried out by using ADAMS software.It shows that the motion of the mechanism is relatively stable and the steering center is not fixed when turning.The stress analysis was carried out by using ANSYS Workbench.The results show that the stress in the rod mechanism is within the allowable stress range,which indicates that the structure of the designed mechanism is basically reasonable.