Modelling and State Estimation in Pulsed ECM with Variable Electrolyte Conductivity

Abstract

In Pulsed Electrochemical Machining the control of the size of the process gap is necessaryto achieve process stability. However, the gap size cannot be measured directly during the machiningprocess. Based on an equivalent circuit, a process model has been derived for plane electrodes andconstant conductivity. In a previous study, an approach to controlling and estimating the gap size hasbeen introduced. By input-output-linearisation, a linear system was found, making it easier to controlthe gap size and current flow simultaneously.In this work the existing model is revised for its applicability to the conductivity change duringeach pulse resulting from heat and gas bubble generation. Depending on the particular moment of thecurrent measurement, the value of the conductivity in the electrolyte reservoir cannot be used for thegap size estimation directly. Three different approaches to overcome this problem are reviewed. Themost promising approach was implemented on a real-time platform and optimised for execution time.