Introduction to Industrial Automation

3.5.4   Automation of a Garage Door

In complex machines, where a recurrent operation takes place, this is commonly achieved through 

the utilization of a motor with the capability of rotation inversion, as has been indicated in Section 

3.4.1. In the current application, the recurrent component is a garage door, which is equipped with 

a motor with reverse capability. As indicated in Figure 3.27, a combined operation of the door 

is necessary through the utilization of two limit switches (b

1

, b

2

) and one photocell-sensor (u). 

The limit switches stop the movement of the door automatically (safety switches) when it reaches 

the corresponding motion limit. The photocell is utilized for the detection of humans, in order 

to instantly terminate the movement of the door upon human detection. The operation of this 

ELS = electronic level switch

Pumps

ELS

2

ELS

1

E

2

E

1

ELS = electronic level switch

N

C

1

50 Hz 230 V

R

e

1

NC 

ELS

1

RS

1

e

2

RS

2

C

2

NC 

ELS

2