Introduction to Industrial Automation

19

Chapter 2

Hardware Components 

for Automation and 

Process Control

2.1   Actuators

An actuator is a device that uses some type of energy and produces the required force, either 

providing motion to an object or actuating something. Actuators (independently of their shape, 

form, and size) produce the mechanical movements required in any physical process in a factory. 

It should be highlighted that in any industrial production line, if the actuators are removed, what 

will remain are only the “passive” metallic and plastic components, while the whole automa-

tion will lose its ability to alter or produce something meaningful. All actuators are controllable 

devices for performing the desired manufacturing operations, in order to have a well-controlled 

and automated production process. In general, there are various kinds of actuators that can be 

categorized based on the operation principle, such as thermal, electric, hydraulic, pneumatic, and 

micro-electro-mechanical (MEMS) ones. Figure 2.1 illustrates a number of different types of 

actuators.

Thermal actuators convert the thermal energy into movement based on various physical prin-

ciples. As an example, a bimetallic strip is one type of thermal actuator made from two different 

metals, such as steel and copper. In this specific case, it is known that the two metals have differ-

ent temperature coefficients, and when they are heated, their expansion occurs at different rates. 

Therefore, two similar strips from different metals, jointed together along their entire length, may 

generate motion at their free end. When heat is applied, the bimetallic strip bends in the direc-

tion of the metal with the smallest thermal coefficient, and deflects enough to energize an electric 

contact, for example. Such a bimetallic strip actuator is used in thermal overload relays, which are 

described in detail in Section 2.2.1.

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