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Automating Manufacturing Systems - Process Control and ...

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plc sfc - 20.4<br />

Start<br />

lock doors<br />

1st digit<br />

OK<br />

1<br />

1st digit<br />

wrong<br />

1st digit<br />

OK<br />

6<br />

1st digit<br />

wrong<br />

2<br />

7<br />

2st digit<br />

OK<br />

2nd digit<br />

wrong<br />

2st digit<br />

OK<br />

2nd digit<br />

wrong<br />

3rd digit<br />

OK<br />

5sec.<br />

delay<br />

3<br />

4<br />

unlock#1<br />

3rd digit<br />

wrong<br />

5 sec.<br />

delay<br />

8<br />

unlock#2<br />

9 relock#2<br />

5 relock#1<br />

Parallel/Concurrent because things happen separately, but at same time<br />

(this can also be done with state transition diagrams)<br />

Figure 20.3<br />

SFC for <strong>Control</strong> of Two Doors with Security Codes<br />

A simple SFC for controlling a stamping press is shown in Figure 20.4. (Note: this<br />

controller only has a single thread of execution, so it could also be implemented with state<br />

diagrams, flowcharts, or other methods.) In the diagram the press starts in an idle state.<br />

when an automatic button is pushed the press will turn on the press power <strong>and</strong> lights.<br />

When a part is detected the press ram will advance down to the bottom limit switch. The

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