Overview of Servo Control

Abstract

The term servo originates from a Latin word servus, which means servant or follower. Along this perspective, a servo control system can be defined as a system that is able to control some variables of interest to track user-specified objectives closely. While the first contribution of servo control has generally been attributed to Ktesbios of Alexandria (ca. 200 B.C.E.) (Mayr, Origins of feedback control, MIT Press, Cambridge, 1970) for his invention of water clock, the continuous history of modern servo control started on 1788, when James Watt invented the fly-ball governor to regulate the speed of a steam engine. Subsequent development and invention of devices such as flow valves and pressure regulators contributed, historically, to the emergence of the Industrial Revolution and, technologically, to the servo control technology. Besides those “hardware” inventions, mathematical techniques and control algorithms were also devised, such as stability theory by Lyapunov around 1890 and frequency-domain analysis around 1920. A major boost to the development in this field came along with World War II, when servo control was used in diverse military applications, including the precise guidance and control of missiles, tracking of military targets, and development of navigational systems.

Today, servo control has become an integral part of almost every automation system or process, including in manufacturing, chemical, petrochemical, transportation, military, and biomedical. While the broad definition of servo control as mentioned above still holds, the expectations in terms of the tracking performance of servo control systems have risen significantly, in line with the ever tightening and stringent requirements associated with the products of today and the processes to achieve them.

This book will focus primarily on servo control in the application domain of motion control systems, although some of the topics covered will remain applicable to other application domains such as in process control systems.