Introduction to Industrial Automation

Figure 1.7  Example of an automatic control system.

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  Introduction to Industrial Automation

level of the liquid in the tank by a level sensor and, subsequently, appropriately tune the outflow 

valve. In this case, the outflow valve has not only two states “Fully Open—Q

max

 flow” and “Fully 

Closed—0 flow”, but it can take any kind of desired state value, thus allowing for a flow within 

the (0, Q

max

) continuous space. In the era of classical industrial automation, this control scheme 

would have been implemented by analog circuits, whereas now it is commonly implemented by 

the utilization of computers and, more specifically, programmable logic controllers (PLCs), which 

are computational devices designed and configured for operating in industrial environments.

In Figure 1.8, a lead screw setup is presented, where the worktable can be translated by the 

proper connection and rotation of the lead screw into two directions (left and right). For this rea-

son, the motor generating the rotation of the lead screw has two directions of rotation. Moreover, 

the motor has two rotation speeds, which means that the worktable can be translated in two speed 

profiles. With the help of the indicated position sensors (limit switches) and the provided motor, 

we can design an industrial automation with the following desired operation. As shown in Figure 

1.8, the  worktable should be continuously moving between the final positions A and D, while 

in the translation space from B to C the table should move at the fast speed and at the low speed 

for the remaining ones. In this setup, there is no continuous variable that needs to be controlled, 

while all the devices have two states of operation, ON and OFF. In this case, the controller is an 

automation circuit, which is responsible for implementing the described sequential (or Boolean) 

control logic, e.g., partially described in the following form:

….When sensor B is energized, the motor should be set (start operating) and remain in 

the fast speed. When sensor C is energized, the motor should be set and remain in the slow 

speed. When the sensor D is energized the motor’s direction of rotation should be inversed, 

without changing the speed of translation….

At this point, it should be mentioned that the aforementioned translational system is not 

described by a specific transfer function, as in the case of automatic control systems, but from a 

Boolean function that expresses the desired operational logic.

Many books in the field of automatic control refer to the sequential control of two states as 

the fundamental form of industrial control, while providing minimum reference to this topic and 

concentrating on the analog and continuous time closed-loop control (feedback control). On the 

contrary, this book will focus on the methods needed for designing and implementing industrial 

automation systems, which cover a significantly larger set of the current trends in the area of 

industrial control systems.

After defining that, in an industrial system, both continuous and sequential control setups 

exist, the term “industrial automation” now has a wider meaning, which includes every kind of 

system being designed for implementing an automatic operation of an industrial process.

Worktable

Work screw

Motor

(n1, n2,         )

Limit

switch

A

B

C

D