By Machine & Scenario — Practical Safety Layouts
Field-proven topologies and checklists for presses, press brakes/shears, robot cells, and AGV/AMR. Built around OSSD/EDM principles, ISO 13855 safety distance, and clean interlocks.
Safety notice: Standard PLCs (e.g., FX5U/S7-1200) are not safety PLCs. The stop path must be: OSSD → safety relay/controller → K1/K2. EDM closes the loop around K1/K2 and blocks unsafe reset.
1) Press retrofit — 3-in-1 feeder & robot interlock
Topology (simplified)
┌──────────┐ OSSD1/2 ┌─────────────┐ K1/K2 ┌──────────┐
│ Light │────────────▶│ Safety Relay│───────────▶│ Contactor│──▶ Motor/Clutch
│ Curtain │ │ (EDM IN) │◀──NC──NC──▶│ Pair │
└──────────┘ └─────────────┘ └──────────┘
▲ ▲ ▲
│ │ └─ Manual Reset (edge-only)
│ └───── Robot cell interlock (MGB/door)
└─ Muting (coil feed) only for auto-feed infeed/outfeed windowsWhen to use light curtains vs hard guarding
- Operator loading/unloading across an opening → Type 4 curtain with proper distance.
- Fully automatic, fenced line → prefer full perimeter guarding, curtain at load station only.
- High oil mist/welding spatter → add protective windows and cleaning SOP.
Interlocks with 3-in-1 feeder & robots
- Feeder RUN permit tied to safety controller SAFE state.
- Robot “safety I/O” (gate/ES) wired as series inputs to the same safety controller.
- Robot auto-mode requires muting active + feeder in “auto window” + no manual reset pending.
Distance & response time
Compute S = K × (t_r + t_s) + C. For presses, re-measure stopping time t_s after any clutch/brake work. Narrower resolution (10–14 mm) increases C and reduces range — select only when finger protection is truly needed.
Commissioning checklist
- OSSD1/2 landed on separate fuses; desync A≠B triggers fault.
- EDM loop returns through K1+K2 NC in series; welded contact blocks reset.
- Muting sensors fixed and timed; no “infinite mute”.
- Test-rod sweep at left/center/right; record results and photos.
2) Press brake / shear — blanking & muting
Application boundaries
- Fixed blanking only for unavoidable obstructions (die fingers) and within standard limits.
- Floating blanking may permit limited beam interruptions; never allow a hand-sized gap.
- Shears: prefer dual-channel two-hand controls or perimeter guarding when feasible.
Recommended layout
Brake Front Opening
[Curtain TX] ⇄ [Curtain RX] (resolution 14/30 mm)
└─ Reset on operator side; full view of hazard zone
└─ Foot pedal interlocked via safety relay (EDM verified)Typical parameters
| Use case | Resolution | Protective height | Notes |
|---|---|---|---|
| Finger pinch protection | 10–14 mm | 500–600 mm | Shorter range; high alignment accuracy |
| Hand/forearm | 30–40 mm | 900–1200 mm | Common for brake front opening |
Validation
- ISO 13855 distance sheet updated; t_s measured with current die and stroke.
- Blanking documented with drawings; risk assessment attached.
- Quarterly inspection with certified test rods (14/25/30 mm).
3) Robot cell — light curtain vs safety scanner
Selection guide
| Scenario | Choose | Why |
|---|---|---|
| Linear access, clear opening | Light curtain | Fast response, simple distance calc, lower cost |
| Curved access or multiple aisles | Safety scanner | Configurable protective fields and warnings |
| Mobile pallet stations | Hybrid | Curtain at load gate + scanner for area |
Scanner zones (example)
┌──────── Protected field (robot stop)
│■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■
│□□□□□□ Warning field (speed reduction)
──┘ Cell perimeter with gates interlocked (MGB)Integration notes
- Robot safety I/O: tie ES/GATE to the same safety controller as curtains/scanners.
- For scanners, use field sets (teach-in) for auto vs manual; log CRCs and configs.
- Reset station outside the cell with full view; rising-edge only.
4) AGV/AMR — zones, speed monitoring & handover
Zone concept
- Protective field stops vehicle; warning field reduces speed.
- Dynamic fields switch based on speed (SIL-rated controller or integrated scanner logic).
- Handover at docking stations: vehicle scanner interlocks with station curtain or door switch.
Docking handover (example)
AGV scanner ──▶ Warning → Slow
└▶ Protected → Stop at dock
Dock door switch (ES) + station light curtain interlocked
Station grants "safe docking" to AGV controllerRecords
- Field set CRC and version saved; change control in place.
- Speed vs stopping distance validation per supplier spec.
- Monthly functional test at docks and blind corners.
5) FAQ
Do I need a safety PLC for these layouts?
Not always. A safety relay/controller is sufficient for many lines. Use a safety PLC when you need complex logic (muting, zone switching, networked robots/AGVs).
Can I share one contactor for both channels?
No. Two independent contactors (K1/K2) with EDM feedback are required to achieve PL e/SIL 3.
How often should I re-measure stopping time?
At commissioning, after drive/brake maintenance, and at least annually for high-demand systems. Update the ISO 13855 sheet each time.