Control system design for a rapid thermal processing system

Abstract

This paper proposes a control system design for a rapid thermal processing (RTP) system, which has four circular concentric lamp zones and four temperature sensors. The control system consists of a least square feedforward controller and an output feedback proportional plus integral (PI) controller. The goal is to maintain uniform temperature tracking for typical ramp-up and hold-steady profiles. A high-order nonlinear model describing the temperature dynamics of the rapid thermal processing (RTP) system is used for the feedforward controller design. A balanced reduced model, obtained from a linear model around a desired uniform steady-state temperature, is used for the design of the multiinput-multioutput (MIMO) PI controller. The PI controller gain matrices are designed using an LQR-based procedure. Tradeoff between robustness and performance of the system is discussed, Simulation results show the control system designed yields robust temperature tracking with good uniformity for a wide temperature range.