Performance Analysis of a Robust Proportional—Integral—Derivative Control Technique for the Auto-Focusing Mechanism of an Optical Surface Profile Measurement System

A control system is regarded as the vital component of a process loop. For centuries, various control techniques have been employed to control actuators or process parameters in an effective manner to obtain the desired response. The field of control engineering has seen phenomenal changes in the past two decades or so, epitomized by the rise of ever-more sophisticated modern intelligent control techniques. However, despite such massive improvements in control techniques, century-old proportional—integral—derivative (PID) controllers are still widely used in industry and research alike owing to the simplicity of fabricating and tuning such devices. Many studies in the literature have shown that a particular variant of the PID controller, namely a robust PID, is even more effective in achieving better performance of the closed-loop system. This paper investigates the performance enhancement of the response of the auto-focusing mechanism of a surface profile measurement system using a robust PID controller as opposed to a controller tuned using the conventional Ziegler—Nichols (ZN) method. It can be observed through the reported results that the use of the former technique helps to achieve the highly desired closed-loop response of fast settling time, reasonable overshoot, loop disturbance rejection, and high system bandwidth of the focusing mechanism.