Control Engineering: Principles and History
What is Control?
It is the action or effect of deciding on the development of a process or system. It can also be understood as a way to manipulate certain variables to make them, or other variables, act in the desired way.
What is Control Engineering?
It is an interdisciplinary approach to control systems and devices. It combines areas such as electrical, electronic, mechanical, chemical, process engineering, and mathematical theory, among others.
Subdisciplines (by Type of Control)
- Open-loop control
- Closed-loop control
- Regulation (set-point control) to maintain a constant
- Tracking of trajectories (to follow something that changes, with minimum error)
Subdisciplines (by Type of Theory)
- Linear control (very small, easy to use)
- Nonlinear control (for complex systems, very effective)
- Optimal control (looks for the best solution within restrictions)
- Robust control (better performance under shocks)
Key Definitions in Control Engineering
System: A combination of components that work together to achieve a certain goal. The system concept can be applied to physical, biological, economic, social, and other phenomena.
Controlled variable (output): The quantity or condition that is measured and controlled.
Manipulated variable: The variable that is modified to affect the controlled variable.
Process: The natural development of an event, characterized by a series of gradual changes, continuous progress, and a tendency towards a final result.
Plant: A set of machinery pieces designed to perform some activity together. In control systems, the plant is the system to be controlled.
Disturbances: Any event that adversely affects the development of a process. If the disturbance is generated within the system, it is called an internal disturbance; otherwise, it is an external disturbance.
Open-loop control system: A control system where the output has no effect on the control action. The output may or may not be measured, but this measurement does not affect the controller.
Feedback control: An operation that tends to maintain a prescribed relationship of one system variable to another by comparing these functions and using their differences as a means of control.
Feedback control system: A control system that uses a relationship between the output variable and a reference variable as a means of control.
History of Automatic Control
Early Applications
The first applications date back to the regulatory mechanism with a floater in Greece.
The Ktesibius clock was built around 250 BC. It is considered the first automatic control system in history.
Heron of Alexandria (100 AD) published a book called Pneumatica, which describes several mechanisms for regulating water levels using floats.
Modern Age in Europe
The first feedback control was built by the Dutchman Cornelis Drebbel (1572-1634). In 1618, he built an incubator with explicit feedback to regulate temperature. But the most significant work was the first useful submarine by Drebbel in 1620, where he also used feedback systems.
Frenchman Denis Papin (1647-1712) invented the first pressure regulator for steam boilers in 1681.
However, the first significant work in automatic feedback control was James Watt’s centrifugal regulator, developed in 1769.
Russia claims the first control system was the water level regulator float invented by I. Polzunova (1729-1766) in 1765.
JC Maxwell (1831-1879) considered a mathematical theory related to control theory using the model of a differential equation in 1868:
His contributions:
- Concept of stability
- Simple mathematical models
- Importance of stability
- Linearization as a problem
- Integrating algebraic stability criteria for first, second, and third-order systems
Evans, in the final decade of the 1940s and the beginning of the 1950s, developed the method of the place of the roots. The methods of frequency response and root locus are the basis of classical control. During this time, Russian scientists focused on the formulation and time-domain differential equations.
Post-War Advances
There was a rapid spread of new control theories, greater openness between Russian and Western theories, the establishment of research centers in control, increased interest in non-combat control systems, more control courses in universities, and public debates about control and other sciences.
The modern theory of control is based on analysis and synthesis in the time domain, using state variables.