Dynamic Investigation of Non-linear Behavior of Hydraulic Cylinder in Mold Oscillator using PID Control Process

To learn the dynamic characteristics of a mold oscillator, we establish a model that describes the relationship between force equilibrium of a hydraulic cylinder and mold under various oscillation conditions. The nonlinearity caused by the servovalue and the operating fluid is considered as excitation, and is calculated as control error between an input signal and mold oscillation in realtime by a PID control process. Based on the nonlinear property, we determine that the dynamic behavior is caused by mold oscillation displacement and hydraulic cylinder pressure. We define excitation frequency and harmonic terms, and determine that the sources of the harmonic peak frequency and high peak frequency; (50n ± exciting frequency ωexc) are friction between the piston and hydraulic cylinder, and variable stiffness of the operating fluid. Finally, a mathematical model of the hydraulic chamber that can represent the unknown non-linear phenomenon is derived.