Multi-cylinder leveling control systems based on dual-valve parallel and adaptive eccentric torque suppression

In the composite material hydraulic press, the mismatched velocities between the movable beam and the multiple leveling cylinders produce disturbing superfluous forces, and the eccentric torque causes the movable beam to tilt when pressed. They severely damage the leveling displacement accuracy and limit the implementation of muti-cylinder system in higher precision field. A dual-loop leveling control strategy is proposed, comprising a dual-valve parallel pressure inner loop and an adaptive control displacement outer loop. Firstly, a dual-valve parallel scheme is proposed in the pressure inner loop, where a compensation valve is added in parallel with the original single-valve. A variable compensation valve spool algorithm is designed, considering both velocity and displacement to mitigate the effects of superfluous forces and achieve precise and smooth leveling. Secondly, a control strategy for the adaptive displacement outer loop is designed to estimate and compensate for eccentric torque. An innovative torque decoupling algorithm is formulated to overcome the challenge of indeterminate coupling relations between inner and outer loops caused by the adaptive incorporation of dual-loop control. Then, eccentric load compensation torque is decoupled to the multiple leveling cylinders and derives the desired pressure for the inner loop. The inner loop suppresses the disturbance of eccentric torque to enhance robust leveling precision. Finally, the effectiveness of the proposed strategy was validated through experimentation on the constructed hydraulic press leveling system test bench. The control strategy presented in this paper provides a reference for achieving smooth and precise control in multi-cylinder systems.