Adaptive Nonlinear Control of the Czochralski Process Via Integration of Second Order Sliding Mode and Iterative Learning Control

Abstract

This paper utilises nonlinear second-order sliding mode (SOSM) combined with an iterative learning control (ILC) scheme for the control of interface dynamics primarily focused on diameter control in the Czochralski (CZ) process. The sliding mode control (SMC) or variable structure control (VSC) is well suited for systems with bounded and unstructured parametric uncertainties. The SOSM is therefore employed to attain robustness in the control despite unknown system dynamics. On the other hand, iterative learning control is incorporated as an intelligent module of the designed controller to better adapt to repetitive operation even in the presence of unknown parameters and bounded disturbances. Since CZ is a batch process that repeats itself every time a new crystal ingot is produced, repeatability renders learnability to the designed controller.