Abstract: In order to investigate the influence of nonlinearity of valve controlled cylinder on the performance of electro-hydraulic servo system, based on electro-hydraulic servo system of pipe expanding procession, firstly the nonlinear character of valve’s electrical signal input to spool position and spool position to cylinder piston displacement output is analyzed, then a nonlinear model on asymmetry cylinder actuated by asymmetry valve is provided to represent the actual system. Secondly, according to two-step character of the actual system model, a nonlinear control approach with quantitative feedback theory (QFT) and perturbation estimation (PE) is put forward to realize the respective control of load motion and load pressure nonlinear dynamics. Finally, compared with conventional PID control, the validity of the proposed control approach is tested by simulation and actual control application. Results show that the proposed algorithm has better dynamic and static response performance. This method provides a useful tool for solving practical engineering problems.

Key words: Nonlinear control, Perturbation estimation, Quantitative feedback theory, heat treatment, heavy Forging, impact toughness, tensile strength, tube sheet, SA508 Gr.3 Cl.2 steel