Introduction to Industrial Automation

Example 4.5:  Combined Operation of Two Machines

Two machines M and N operate through the action of a pushbutton b and two sensors s

1

 and s

2

, 

according to the following specifications:

 

a.  By pressing the push button b once, the machine M starts to operate.

  b.  By pressing button b for a second time, the machine N starts to operate, while the machine 

M continues to operate.

  c. If both machines operate and sensor s

1

 is energized, then the machine M stops, while the 

machine N continues to operate. If instead of sensor S

1

, sensor S

2

 is energized nothing must 

happen.

  d.  If only the machine N operates and sensor S

2

 is energized, then the machine N stops also.

The state diagram, shown in Figure 4.14, has been designed based on the assumption that the 

first activation of the button b leads the system to the state S

1

 and it remains there for as long as time 

is required. Similarly, the second activation of the same button b causes the transition from S

1

 to 

S

2

, where both machines are in operation. The introduction of two auxiliary variables and the code 

assignment, shown in Figure 4.14, give the following equations:

 

A

s B)(bB A)

=

+

+

(

2

 

B

s A bA B

=

+

+

(

)(

)

1

 

M AB AB B

=

+

=

 

N AB AB A

=

+

=

By converting these Boolean expressions into an automation circuit, the circuit shown in Figure 

4.15 is obtained.

S

0

S

1

b

s

2

S

2

b

s

1

Μ=0

Ν=0

Μ=1

Ν=0

Μ=1

Ν=1

S

3

AB

00

Μ=0

Ν=1

01

11

10