Introduction to Industrial Automation

Figure 4.21  The final automation circuit of Figure 4.20, after simplification.

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  Introduction to Industrial Automation

The synthesis of a component-based state diagram, following the above rules, leads to a star 

form diagram with state S

0

 in the center and states C

i

 around S

0

. The system’s states are then 

various sets of states C

i

. For example, a system state S

1

 may be the set {C

1

, C

3

, C

4

}, while another 

system state e.g., S

3

 to be the set {C

1

, C

2

}. Let’s explain the composition of the component’s state 

diagram by the use of an example.

Example 4.9:  Automation of a Multi-Conveyor Assembly Station

Consider the assembly station shown in Figure 4.22. From three locations A, B, and C of initial pro-

duction, three corresponding objects are sent via the central conveyor D to the assembly table. The 

conveyors A, B, and C operate continuously and are therefore not considered in this automation system. 

Each of the three workers always puts the same object on the conveyor, for which they are responsible at 

random times, but only under the condition that the corresponding light H

1

, H

2

, or H

3

 is on. When an 

object reaches the conveyor D, it is detected by the corresponding proximity switch (PS

i

) and then the 

corresponding light (H

i

) turns off, indicating that another object should not be placed on the conveyor. 

There is no specific order for the placement of the three objects from the workers. When the last object 

reaches the conveyor D, this means that there are three different objects on the central conveyor D. 

First, the light H

4

 turns on, and second, the central conveyor D can operate if the worker at the assem-

bly table presses the button b

0

. After the button pressing, the conveyor D operates for 45 s. At the end 

of this period the conveyor D stops, the lights H

1

, H

2

, and H

3

 turn on while the light H

4

 turns off.

The digital components of the system are four lights, the motor for operation of the central conveyor 

D (powered by the relay C

M

), and a timer T, required to measure the operation time of 45 s. Therefore, 

the component-based states of the system are: {C

1

 for H

1

}, {C

2

 for H

2

}, {C

3

 for H

3

}, {C

4

 for H

4

}, and {C

5

 

for C

M

 and T}, since the timer T and the relay C

M

 are identical from the operation point of view. The 

component state diagram is shown in Figure 4.23, where the transition to state C

i

 for i=1 to 3 is triggered 

by the corresponding signal PS

i

, and may happen simultaneously. The transition to state C

4

, where H

4

 

is ON, depends on the condition C

1

C

2

C

3

, which means that three objects are ready to be placed on the 

conveyor D. The transition to state C

5

 is triggered by the condition b

0

C

4

, which means the state C

4

 is 

energized and the button b

0

 is pressed. Subsequently, we can write the logical equation (1) for all states C

i

.

 

Turn ON C

PS

Turn OFF C

T

Turn ON C

PS

Turn O

1

1

1

2

2

=

=

=

FFF C

T

Turn ON C

PS

Turn OFF C

T

Turn ON C

C

2

3

3

3

4

=

=

=

=

11 2 3

4

5

0

4

5

C C

Turn OFF C

T

Turn ON C

b C

Turn OFF C

T

=

=

=

A

B

C

PS

1

A

B

C

D

A

B

C

D

H

1

H

2

H

3

H

4

b

0

A

B

C

PS

2

PS

3

D

As

sem

bly

tabl

e