Research Of Force-Position Combined Control Technology For Tractor Electrohydraulic Hitch System

With the developing trend of tractor design to be intelligent and lightweight, the use of micro-electronic technology and control technology is an inevitable way to tractor. The traditional mechanical control system in tractor is being replaced by electro-hydraulic hitch system gradually.Based on the traditional hitch system, the paper designed a tractor electro-hydraulic hitch system which had force-position adjust function. Compared to the traditional hitch system, the new system used electronic control technology to achieve the displacement regulation of tillage depth and force regulation. The control chip collected the real time signals from force sensor and position sensor, then controlled the flow of the electro-hydraulic proportional valve, raising or dropping the hitch poles. The electro-hydraulic hitch system leaved out the original manual control poles, reduced the degree of manual working difficulty and gave a solution to the imprecision of tillage depth.On the part of the hydraulic system, electro-hydraulic proportional valve was used as hydraulic actuator. Three-way pressure compensator used together to control hydraulic flow exactly. The schematic of hydraulic system was designed. This paper established the simulation model of the hydraulic system based on Amesim software, verified the correctness of the system and conducted a simulation analysis of dynamic characteristics.Considering about the mechanical part of tractor hitch is a nonlinear control system and other problems such as response lag, interference factors, we can’t set up the precise mathematical models easily. The fuzzy control theory can achieve intelligent control without the precise mathematical models, so we chosen fuzzy control theory to design controller.On the part of hardware design, TMS320F2812was chosen as control chip. This paper introduced the hardware structures and functions of the chip, and designed minimum hardware system. About the interface circuit design of sensor and actuator, this paper finished the signal collections of force sensor, position sensor, speed sensor and PWM signal output.On the part of software design, this paper used C language to write module program based on the characteristic of TMS320F2812. The use of head file simplified the work of main program design. The paper designed the main program, including lifting and dropping subroutine, force-position combined adjustment subroutine, fuzzy control module, PWM output subroutine and safety testing module.In conclusion, the testing of the whole system gained good curves of power adjustment and position adjustment. The corresponding PWM wave shapes of electro-hydraulic proportional valve were also given out. The experiment result showed that the controller achieved the design requirements.