An application of adaptive control techniques in metrology

This paper examines the dynamic performance of an automated optical gauging instrument. A mathematical model of the system is developed which demonstrates the intrinsically non-linear characteristics which provide coupling between two nominally independent control loops. Approximate stability bounds for the closed-loop system are established using the describing function matrix technique. The inverse Nyquist diagram is used to design appropriate compensation networks, taking into account design objectives including the avoidance of various limit cycles and a rapid transient response. The final design is implemented on the instrument and its behaviour compared with the simulated system. It is shown that the response time is reduced to approximately 11% of that of the original system in agreement with design predictions.