Position control using a digital servo system

Abstract

[Abstract]: This report details an investigation into the performance of some conventional digital control strategies when applied to the problem of position control. The investigation is based on an existing DC motor servo system. A mathematical model of the system has been developed and used for designing various forms of feedback controller. The system has been simulated with each feedback scheme in place and, in the case of the PID controller, physical experiments were performed. State-variable feedback was found to be the most successful and most versatile. While the feedback schemes were successful in providing closed-loop control of the system with desirable response characteristics, the experiments showed that the system lacked rigidity against disturbing forces. This is a problem that must be addressed in most industrial applications of position control and further review of the literature showed that it is a problem inherent to controller designs based on analysing the system only in its linear region of operation. From observations made during this research, it seems that the controller design techniques established on linear control theory, which are presented here, are not well suited to position control, despite the fact that many authors treat them as though they are.