Research On Agricultural Machinery Path Tracking Control System Considering Input Saturation

With the development of society,agriculture,as a pillar and foundation industry supporting the national economy,inevitably needs to keep pace with the times.In2018,the Chinese government once again put forward precise policies to promote the rural revitalization strategy,advance agricultural modernization,and promote agricultural revitalization.This requires China to actively promote the development of precision agriculture.The goal of precision agriculture is to improve agricultural production efficiency,and the popularization and application of agricultural machinery greatly improves operational efficiency.The emergence of unmanned agricultural machinery,in particular,has opened up a path for China to enter a precision agriculture society.In particular,path tracking technology is one of the important technical means to achieve autonomous driving and intelligent operation of unmanned agricultural machinery.It is of great significance for the intelligent,precise,and information-based development of agricultural machinery.The development of path tracking technology,which is currently gaining momentum,has injected new vitality into the automatic driving system of unmanned agricultural machinery.As one of the key components of the agricultural machinery automatic driving system,it has the advantages of reducing labor consumption and improving production efficiency.However,the development of domestic unmanned agricultural machinery path tracking control technology started relatively late,and its control efficiency and stability urgently need to be improved.At present,there are still some problems in the research of agricultural machinery path tracking control system.This article will conduct the following research on these issues:(1)To conduct research on the path tracking control system of agricultural machinery,mathematical modeling is carried out based on vehicle kinematics theory for modules related to obtaining vehicle state information and controlling front wheel steering.In order to achieve more accurate path tracking control,the actual control requirements are analyzed,and the system is simplified accordingly.First,coordinate systems are established with the ground and the agricultural machinery body as the centers.Under the established coordinate systems,the agricultural machinery vehicle itself is simplified into a two-wheel vehicle model(bicycle model),with the front and rear wheels as centers,and the control variables of front wheel steering angle,travel speed,and agricultural machinery heading angle are introduced.Based on the geometric relationship between the front and rear wheels,the kinematic model of the agricultural machinery control system is obtained.(2)Taking into account the practical requirements of path tracking control for agricultural machinery,the deviation between the actual trajectory of the agricultural machinery and the reference path is of key importance.Based on the kinematic model of agricultural machinery,the lateral deviation and heading deviation are chosen as state variables,and the reference path is represented in the form of curvature.A path tracking deviation model for agricultural machinery based on deviation is established.In addition,to more accurately describe the complexity of the agricultural environment during actual operations,the uncertainty factors of the agricultural environment are simulated,and a time-varying disturbance is introduced into the system to obtain a disturbancebased path tracking deviation model for agricultural machinery.(3)To address the actuator saturation problem in the agricultural machinery control system,a nested saturation controller is designed.Firstly,a linear controller is designed to ensure the local stability of the system within a certain region.Secondly,in order to solve the problem that the saturation degree of the saturation function may not increase but change with time during the actual control process,the saturation function is combined with the linear controller to construct a nested saturation controller.Compared with traditional saturation controllers,the nested saturation controller designed in this research has more flexible selection of saturation degree,better stability,and robustness.Furthermore,a composite control method is proposed by combining sliding mode observer and bounded controller.By combining the sliding mode observer with the bounded controller,the control system has better adaptability to external disturbances.(4)The nested saturation algorithm based on linear system design cannot fully apply to practical systems with nonlinear characteristics.To better suit the nonlinear characteristics of the agricultural machinery path tracking control system,a finite-time nested saturation control algorithm based on nonlinear system is designed.The finitetime nested saturation algorithm designed using a two-step approach can significantly shorten the system’s response time and improve its anti-interference ability and steadystate performance.Simulation results show that the finite-time nested saturation control algorithm based on nonlinear system design has better dynamic performance and disturbance rejection ability,and has more obvious advantages over the nested saturation control algorithm.(5)The effectiveness of the agricultural machinery path tracking control system was verified through the design of a finite-time nested saturation control system.Firstly,the YUNLE NWD01 unmanned vehicle test platform was introduced,and specific software and hardware design schemes were provided.Secondly,the path tracking system algorithm was applied to the YUNLE unmanned driving system through programming development,and the navigation positioning,attitude measurement,and line control steering system were modified according to actual control needs to build a complete real vehicle test platform.Finally,a test site was selected to simulate the field environment for testing.The results showed that the test vehicle could complete the tracking process in a short time,and the lateral deviation of the on-line path tracking could be maintained within a certain range,indicating that the control algorithm studied in this paper could meet the accuracy requirements of path tracking control in agricultural field operations and comply with the standards of unmanned agricultural machinery automatic driving control systems in modern precision agriculture.