The Variable Hydraulic Stiffness Compensation in the Electro-hydraulic Position Control System for a Four-High Strip Mill

摘要

The electro-hydraulic servo position control (HPC) system is the core of an auto gap control for a modern four-high strip mill. The hydraulic stiffness is nearly the reciprocal of the displacement in the actuator. For an actuator with a piston diameter of 0.965m the stiffness varies from 102GN/m to 20GN/m as the piston moves from 10mm to 50mm with the oil bulk modulus of elasticity, 1.4GPa.The decrease of the stiffness makes the response time increase and the stabilities bad. In this paper, the relationship between response time and the displacement of the piston and other characteristics of the HPC were analyzed. At the aim of a constant response time of the whole control system, the compensated construction was discussed by introduction a positive differential feedback of displacement With the model simulation an algorithm applied to improve the system responses were developed. The selections of model parameters were also discussed- The simulations show that variations of the rise time are not over 6%. Finally, the industrial experimental data was given.