12.05.2014 Views

Automating Manufacturing Systems - Process Control and ...

Automating Manufacturing Systems - Process Control and ...

Automating Manufacturing Systems - Process Control and ...

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

plc states - 12.5<br />

Red<br />

Yellow<br />

Green<br />

North/South<br />

L1<br />

L2<br />

L3<br />

Walk Button - S1<br />

Red<br />

Yellow<br />

Green<br />

East/West<br />

L4<br />

L5<br />

L6<br />

Walk Button - S2<br />

Figure 12.4<br />

Traffic Lights<br />

The first step for developing a controller is to define the inputs <strong>and</strong> outputs of the<br />

system as shown in Figure 12.5. First we will describe the system variables. These will<br />

vary as the system moves from state to state. Please note that some of these together can<br />

define a state (alone they are not the states). The inputs are used when defining the transitions.<br />

The outputs can be used to define the system state.<br />

We have eight items that are ON or OFF<br />

L1<br />

L2<br />

L3<br />

L4<br />

L5<br />

L6<br />

S1<br />

S2<br />

OUTPUTS<br />

INPUTS<br />

Note that each state will lead<br />

to a different set of outputs.<br />

The inputs are often<br />

part, or all of the transitions.<br />

A simple diagram can be drawn to show sequences for the lights<br />

Figure 12.5<br />

Inputs <strong>and</strong> Outputs for Traffic Light <strong>Control</strong>ler

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!