| In order to analyses the necessity and practicability of the friction welding electro-hydraulic proportional computer close loop control system, three kinds hydraulic systems of friction welding machine, which different from the main control valve by switch reducing valve, proportional relief valve and proportional reducing valve, are established. Friction welding computer control system hardware based on industry PC is designed, and the control software is developed in Windows 2000/XP opening platform by Visual C++ development tools.The static and dynamic characteristics of the three hydraulic systems of friction welding machine are measured and compared by computer control system. Dynamic mathematical model of proportional system is studied, through analyzing physics meaning, simplified model is established by mechanism analytic method. By time domain step response experimental modeling method and frequency domain response experimental modeling method, approximate coarse transfer function is constructed, check analysis is carried out in Matlab environment. The results show that the static and dynamic characteristics of the two proportional valve system's axial pressure are good than those of the switch valve system. Proportional relief valve is considered as a second order oscillator node, damping of proportional direction valve and pipeline, and hydraulic cylinder volume effect is an inertia node, and the proportional relief valve system construct by the two nodes in series. Proportional reducing valve system has nonlinear character similar to loop delay, from the time domain step response analysis, the system can be simplified to second order oscillator model, and system changes from underdamping, critical damping to overdamping system with the proportional direction valve's flow changes from high to low. Mass production is welded individually in the three systems, and the key welding parameters stability and changing tendency are compared, the influence of oil temperature variations to axis force and other parameters is analyzed selectively. Oil temperature variations effects axis force stability of switch valve system higher than that of proportional system, and the oil temperature higher, the force lower. The electro-hydraulic proportional computer closed-loop control system remove the influence of oil temperature variations and other factors to axis force stability. In long period welding production, friction force and upset force's average error of proportional control system is zero, standard deviation and coefficient of variability is lower one order than that of valve control system. Other key parameters, state current, deformation etc. of proportional control system is more steady. But work velocity in proportional system changes more, some improvement is wanted.
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