Fast and Stable Electrical Discharge Machining (EDM) by Two-step-ahead Predicted Control

In order to improve EDM performances, the most important issue is to develop a highly stable control system. As to a serious defect of instability in EDM machining even in EDM adaptive control systems by Minimum-variance (MV) control this paper focuses on stabilizing EDM process by extending the MV control to minimum-variance and pole-placement coupled (MVPP) control and two-step prediction (TSP) control. Based on real-time estimation of EDM process model parameters, the latter two control systems directly control electrode discharging cycle not only to follow a specified gap state for fast machining but also to track the dynamical response of a reference model for stabilizing machining processes. The experiments specially designed demonstrate that both control systems can timely adjust electrode discharging cycle in terms of different machining situations quantified as a series of varied gap states to maintain a stable and fast fabrication, while the TSP control performs even better. The adaptive control systems by the two controls exhibit superior machining ability and capability of stabilizing sparking process to the adaptive control system by MV control. The two control laws have actually theoretically and technically solved a stability issue puzzled in EDM circle for decades.