8
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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
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