Automating Manufacturing Systems - Process Control and ...

plc software - 32.9
"What information does the system need?"
"What information does the system produce?"
When possible a large controls problems should be broken down into smaller problems.
This often happens when parts of the system operate independent of each other. This
may also happen when operations occur in a fixed sequence. If this is the case the controls
problem can be divided into the two smaller (and simpler) portions. The questions to ask
are;
"Will these operations ever occur at the same time?"
"Will this operation happen regardless of other operations?"
"Is there a clear sequence of operations?"
"Is there a physical division in the process or machine?"
After examining the system the controller should be broken into operations. This
can be done with a tree structure as shown in Figure 32.5. This breaks control into smaller
tasks that need to be executed. This technique is only used to divide the programming
tasks into smaller sections that are distinct.
Press
Conveyor in Press Pickup bin
part detected
advance
bin replaced
full detect
adv./retract
idle
part detect
advancing
retracting
Figure 32.5
Functional Diagram for Press Control