| Heavy tractor is an important power platform in modern agricultural large-scale production.Studying the automatic control technology of tilling depth in complex working environment is an important branch of intelligent agricultural machinery and equipment.At present,the research on the method of depth adjustment in China is still based on single or double parameters.The automatic control scheme of tilling depth under multi-factor regulation has not been studied in depth.So takes heavy tractor working unit as the research object,comprehensively considers the complicated farming environment,this thesis constructs a multi-parameter mixed automatic adjustment scheme with force-position mixed adjustment as the main line and slip rate adjustment as the threshold.And its control algorithm is discussed in depth.According to the functional requirements of the tilling depth control system,and based on the electro-hydraulic suspension system,the hydraulic system is designed,and the electro-hydraulic proportional control valve,sensor and other key components is selected at first.And based on the analysis of the control principle and coupling method of the new regulation scheme,the rationality and feasibility of the mixed automatic adjustment of force-position-slip are demonstrated.What’s more,the mathematical models of the hydraulic system,suspension unit and sensors are established.And combined with the working characteristics of the whole machine,the force of the whole working unit is analyzed and the relationship between the driving wheel slip and the traction force is discussed.Aiming at the strong nonlinear characteristics of tractor working unit,the characteristics of various control algorithms are compared and analyzed.And the theory of variable domain control is introduced and the design of variable domain fuzzy PID controller is completed.Then,the response characteristics of PID control,fuzzy PID control and variable universe fuzzy PID control are compared and analyzed by Matlab/Simulink simulation platform.It is verified that the response time of the variable universe fuzzy PID controller is short and there is no overshoot phenomenon.And It can respond quickly to abrupt signals and can reach a new stable state in a short time,with good response characteristics and anti-interference performance.Based on the variable domain fuzzy PID control algorithm,under the specific environmental conditions,the simulation curves of two depth adjustment methods are analyzed when the average soil specific resistance is 3 N/cm2,4 N/cm2 and 5 N/cm2.Then,the simulation curves of two schemes are discussed when the weighting coefficient is 0.25,0.5 and 0.75 respectively.Finally,the simulation curves of different depth adjustment schemes is verified when the ground is wet and good.By comparative analysis under various variables,it is verified that the mixed automatic adjustment of force-position-slip can adapt to the complex and variable plowing environment.Combined with the existing test conditions,the design and development of the main program and main module sub-programs of the control system were completed based on STMS32F407ZGT6.Then,the field plowing test platform was established.And the field comparison test is carried out to verify the excellent performance of the controller and the depth adjustment method.The results showed that the multi-parameter mixed automatic adjustment scheme based on the variable universe fuzzy PID control can achieve the expected function. |
