Study On Slip Rate Control Of Heavy Tractor For Ploughing Based On Sliding Mode Variable Structure Control

Heavy tractor ploughing unit is the most important power machinery in field production of general field crops in the North.Due to the influence of complex soil environment and great fluctuation of working load,it is so easy to increase excessive slipping of tractor driving wheel.It not only reduces the efficiency of heavy tractor operating unit's field work,but also destroys the growth environment of crops.At present,there is relatively little research on the slip rate automatic control of heavy tractor ploughing unit.Therefore,on the basis of fully understanding the current research status at home and abroad,the research of slip rate control method of the heavy tractor ploughing unit with electro-hydraulic hitch system has been carried out systematically focusing on the ploughing operation condition of field crops.The main contents of this paper are organized as follows:(1)Firstly,the development trend,the key technologies and research methods adopted in domestic and foreign research have been compared and analyzed,according to a large number of literatures and applications of domestic and foreign products.Then the main problems in the measurement and identification method,mathematical modeling,control strategy and algorithm of tractor slip rate control have been proposed respectively.Finally,the research contents and the main technical route of this paper have been put forward.(2)The kinematic relationship between the components of the tractor operating unit was analyzed,with taking the electro-hydraulic hitch system as the research object.Then The force balance and moment balance equation were established by analyzing the force of hitch mechanism,wheel and tractor body.At the same time,some model simplification and mathematical modeling of hydraulic system have been completed.Subsequently,a nonlinear dynamic model of heavy tractor ploughing unit for slip rate control was established based on the characteristics of electronic hydraulic hitch automatic control system,and its motion characteristics was analyzed by Matlab/Simulink.It provided theoretical basis for the further research of slip rate control.(3)In order to guarantee traction efficiency and agronomic requirements,the demand for slip rate control with different ploughing operation modes under full working conditions were analyzed based on the traction characteristics of the heavy tractor operating unit.Then a comprehensive slip rate control strategy has been proposed,In which,setting slip rate as the main control target and taking consideration of the uniformity of the ploughing depth.In view of the strong nonlinear characteristics of the system,the slip rate nonlinear control algorithm based on the sliding mode variable structure control theory has been designed by using the exponential approach law,and verified by off-line simulation.(4)To satisfy functional requirements of electro-hydraulic hitch control system,both the controller hardware and software system have been completed.The hardware in loop simulation test platform was set up based on dSPACE,and the performance of the developed controller was tested.Under different input disturbance and control target,comparative experiments were carried out between the sliding mode variable structure control and fuzzy PID control.The experimental results have verified the superiority and robustness of the nonlinear control method of sliding mode variable structure control.(5)According to the actual working conditions,an automatic slip rate control test platform was built on Foton Lovol TG1254 tractor after sensors' selection and installation.Then field experiments were carried out with different control strategies.The effectiveness of the proposed control strategy and sliding mode variable structure control algorithm of slip control has been verified.The research plays an important role in improving the accuracy of nonlinear control of slip rate.Meanwhile,the practical application is further developed with increased the consideration of agronomic for ploughing depth.The research can serve as a technical reference for the further design and development of the slip control of heavy tractor ploughing unit in China.