| With the development of mechatronics, electro-hydraulic proportional technology has been rapidly developing, electro-hydraulic proportional technology widely used in the control system of present engineering vehicle. The loader is an main engineering vehicle for infrastructure, so it is important and urgent to improve the control system performance and simplify the operating process. Especially electro-hydraulic proportional have a major advantage to instead of relying solely on hydraulic for the poor working conditions and long work frequently. Which not only reduces the labor intensity, more importantly, improve the operation precision to bring production efficiency.In the commutation process, pilot handle is affected by the spring force, hydrodynamic force, friction and other factors, and with the increasing of the power and flow, which will not only increase the operating force, but the operator are also easily fatigued, Especially the pilot handle have a certain pressure range, the pilot control pressure of main valve and the pilot can't match, the system may cause a sudden increase or decrease of flow, which causes a sudden impact on bucket and boom.This is very harmful to the system.So the system use electronic technology to control the pilot pressure, the sensor technology and PWM can control precisely electro-hydraulic proportional valve. So this paper separately introduce hydraulic control and electric control.The hydraulic system of loader mainly consist of bucket and boom, the bucket and boom are driven by two asymmetric hydraulic cylinder. As actuator of the loader, characteristics and control performance of the asymmetric hydraulic will have a direct impact on loader. Therefore, this paper model the proportional directional valve and valve cylinder, and analyze model of hydraulic system using Simulink, mainly analyze static and dynamic characteristics of the hydraulic system. Hydraulic system also includes the proportional pressure reducing valve, which is a bridge of hydraulic system and electric control system, and is core of electro-hydraulic proportional control system. First, the paper analyze the performance of hydraulic valve, then establish mathematical model of the proportional valve and analyze dynamic characteristic using,finally, analyze solenoid control features.the major electrical control proportion of working device to have a proportional pressure reducing valve and two proportional directional valves to control of bucket and boom. this paper introduce three different control methods in order to achieve precise control, then compare their control effect and choose the best one. First, the paper analyze current signal of proportional in time domain and frequency domain and study the control features to prepare for the design for the control system. Then according to the signal analysis, the three control methods, open loop control system, analog PID, software PID, are designed and analyzed. Open-loop control system include hardware design and analysis of performance, and mainly analyze influence of the hydraulic system and anti-interference ability. Analog PID create a closed loop system using proportional current form as a feedback, PWM is generated using triangular and output voltage of PID comparison to drive the proportional valve. This section includes hardware design and simulation with PSPICE,it is useful for analysis of the control process. Software PID control mainly used STM32F103 and uC/OS-II to achieve PID control instead of hardware,this method masterly use PWM module of microprocessor to simplify the control system and optimize PID control system to improve stability.Finally, three control methods were tested to examine performance and dynamic response of the electrical system and hydraulic system control, and observed the stepping response of the control system and the system saves anti-interference ability. By observing experiments, compare their advantages and disadvantages of three control methods and select best one.
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