GRAFCET / SFC
IEC 60848 GRAFCET and IEC 61131-3 sequential function charts: numbered steps with their actions, transitions with their receptivities, and the divergences and convergences — both alternative (OR) and simultaneous (AND) — drawn with the correct single and double bars. Initial steps get their double border, and the engine checks the well-formedness rule every hand-drawn SFC violates: steps and transitions must strictly alternate.
In the same space
Most users come to GRAFCET / SFC from CODESYS SFC editors, Visio GRAFCET stencils or Hand-drawn sequence charts. flowss runs this engine in the browser — no install, shareable via URL, exportable to PNG / SVG / PDF / source.
Sample templates
All 10 →An eight-step filler cycle from bottle index through nitrogen purge, fill and capping, resolving the question every filler argues about — what happens to a bottle whose cap torque fails — with an alternative divergence that routes it to the rework lane and returns both paths to the idle step.
The safety sequence a lift door cannot be certified without: dwell, close, and the alternative divergence on the closing step that sends a photo-eye or door-edge trip to a re-open step and back to the dwell timer, so the interlock is only made when the closed limit and the lock both prove.
The changeover every SMED study starts with, drawn honestly: a simultaneous divergence runs the swing arm and the magazine index at the same time and a convergence of the same width holds the drawbar until both prove, which is exactly the internal time a single-threaded chart hides.
A charge-heat-hold-cool-discharge batch that carries both branch shapes at once: a simultaneous divergence brings the jacket to temperature while the agitator ramps to shear speed, one convergence releases the hold, and an alternative divergence on the assay sends a failed batch round a rework hold rather than out of the vessel.
Ticket or season card, then raise, hold and lower: two alternative divergences and the alternative convergence between them resolve the barrier's two real arguments — which credential opened it, and what stops it descending onto a vehicle still standing on the safety loop.
A vision-gated SCARA cell that carries both bars in one chart: the inspection step diverges alternatively on the vision verdict, and the pass branch opens a simultaneous divergence so the arm picks while the tray indexes, closed by a convergence of the same width that will not release the place until both prove.
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