Connect steps

Once the process steps are defined, connect them together using sequences, simultaneous branches, and selected branches.
If you want to
Then organize the steps like this
With these considerations
Execute 1 or more steps in sequence:
  • One executes repeatedly.
  • Then the next executes repeatedly.
Sequence
connect_steps_seq
  • A step can be used more than once.
  • The controller checks the transition at the end of the step:
    • If true, the controller goes to the next step.
    • If false, the controller repeats the step.
Execute 2 or more paths of steps:
  • Each path executes at the same time.
  • All paths must finish before continuing the SFC.
Simultaneous Branches
connect_steps_sim_branch
  • The bottom of the structure is a single transition.
  • The controller checks the ending transition after the last step in each path has executed at least once.
Decide which path to execute depending on logic conditions:
  • Execute 1 of many paths of steps depending on logic conditions
  • Execute a path of steps or skip the path depending on logic conditions
Selected Branches
connect_steps_sel_branch
  • A path may have a transition and no steps. This lets the controller skip a path.
  • By default, the controller checks from left to right the transitions that start each path. The controller takes the first true path.
  • Logix Designer
     software allows changing the order in which the controller checks the transitions.
Examples
Examples of SFC structures for different situations are:
Situation
Solution
Station 45 and 46 of an assembly line work on parts simultaneously. When both stations are done, the parts move down 1 station.
Simultaneous Branches
connect_steps_sim_branchEx1
Depending on the build code, a station either drills or polishes.
connect_steps_sel_branchEx
Call Out 1
Drill
Call Out 2
Polish
To simplify programming, separate communication and block transfers from other control logic. All occur at the same time.
Simultaneous Branches
connect_steps_sim_branchEx2
Call Out 1
Control
Call Out 2
Communication
Call Out 3
BTs
In a heat treating area, the temperature ramps up at a specific rate, maintains that temperature for a specific duration, and then cools at a specific rate.
Sequence
connect_steps_seqEx1
Call Out 1
Ramp
Call Out 2
Maintain
Call Out 3
Cool
At station 12, the machine drills, taps, and bolts a part. The actions occur one after the other.
Sequence
connect_steps_seqEx2
Call Out 1
Drill
Call Out 2
Tap
Call Out 3
Bolt
Step 12 inspects a process for the correct mix of chemicals.
  • If OK, then continue with the remaining steps.
  • If not OK, go to the top of the SFC and purge the system.
connect_steps_step12Ex
Call Out 1
Start of SFC
Call Out 2
Step 12
Call Out 3
Not OK
Call Out 4
OK
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