Press line retrofit (3-in-1 & robot)
System topology, interlocks, and E-stop loops. This guide shows how to upgrade a mechanical press line using a 3-in-1 feeder (decoiler + straightener + NC feeder) and a robot pick-and-place cell — while meeting Type 4 / PL e safety goals. You’ll get wiring patterns, interlock logic, timing references, and audit-ready checklists.
Safety boundary: Power-removal is executed by a safety relay/controller driving force-guided contactors K1/K2. PLCs/robots only provide status and interlocks; they must not perform the stop function.
1) Line topology (high-level)
Coil → 3-in-1 Feeder → Infeed Guard → Press (ENC) → Outfeed Guard → Robot Cell → Out Conveyor
[Safety devices]
- Infeed: Safety light curtain (Type 4), gate switch on maintenance door
- Press point of operation: Safety light curtain with EDM; optional blanking/muting during feed
- Robot area: Safety laser scanner (zones) or safety fence with interlocked doors
- Global: Emergency stop (E-stop) chain, mode selector (AUTO/SETUP/JOG), safety PLC/relay + K1/K2
ENC = press encoder; provides top-dead-center (TDC) signals and feed windows.
2) Safety devices & zones
Light curtains (infeed / POI)
- Dual OSSD with EDM feedback via K1/K2 NC series.
- Resolution by risk: 10 mm (finger), 30–40 mm (hand), verify protective height.
- ISO 13855 for safety distance:
S = K×T + C; archive calculations.
Robot cell boundary
- Safety scanner with protective/warning fields and speed/zone switching, or fence + door interlocks.
- Teach reduced speed in SETUP; enable high speed only when boundary clear and doors closed.
3) Core interlocks (press, feeder, robot)
| Interlock | Condition | Effect | Notes |
|---|---|---|---|
| Press enable | All safety channels OK + EDM OK + mode valid | Energize K1/K2; allow clutch engage | Gate/curtain/scanner any fault → de-energize |
| Feed window | ENC window active | Allow NC feeder advance | Blocks feed outside window; prevents die crash |
| Robot interlock | Press at safe state (brake set or top position) | Allow robot enter press area | Mutual exclusion with press motion |
| Die-change mode | SETUP mode + reduced speed | Robot & feeder inhibited; jog only | Requires hold-to-run and enabling device if applicable |
Minimal logic (illustrative ST)
// Safety status
LC_OK := (OSSD_A AND OSSD_B AND EDM_FB);
ROBOT_ZONE_CLEAR := ScannerProtective == FALSE;
// Interlocks
PRESS_ENABLE := LC_OK AND DOORS_CLOSED AND ESTOP_HEALTHY AND MODE_AUTO;
FEED_PERMIT := PRESS_ENABLE AND ENC_FEED_WINDOW;
ROBOT_PERMIT := PRESS_AT_SAFE_POS AND NOT PRESS_CYCLING;
// Mutual exclusion
IF ROBOT_PERMIT THEN PRESS_START_CMD := FALSE; END_IF;
IF PRESS_ENABLE AND PRESS_START_CMD THEN ROBOT_RUN := FALSE; END_IF;Replace with your safety-rated function blocks. PLC code is supervisory only; power removal is via safety relay/PLC + K1/K2.
4) E-stop loops & power hierarchy
Hierarchy
- Category 0 (hard stop): Mains contactors open; motion power removed.
- Category 1 (controlled stop): Commanded decel then remove power.
- E-stops in any zone must de-energize K1/K2 for the whole hazard they protect.
Loop concept (ASCII)
E-stop PBs ─┬─► SRELAY CH_A ─► K1
└─► SRELAY CH_B ─► K2
EDM (K1/K2 NC) ────────────────► SRELAY FB
Aux status ────────────────────► PLC/Robot5) Timing: encoder, feed window, muting
- Use press encoder to define feed window (e.g., 210–350°). Block feeder outside window.
- Light curtain muting/blanking only when material entry is unavoidable and risk assessed.
- Record response times: light curtain, safety relay, contactors; verify worst-case meets
S=K×T+C.
6) Copy-ready I/O map (generic)
| Tag | Source/Device | Purpose | Notes |
|---|---|---|---|
OSSD_A / OSSD_B | Infeed/POI light curtain | Safety channels | Independent harness/fuse |
EDM_FB | K1/K2 NC series | Welded-contact detection | Blocks reset |
DOOR_OK | Gate interlock switches | Boundary closed | Redundant contacts |
SCANNER_SAFE | Robot area scanner | Zone clear | Protective field |
ENC_TDC / FEED_WIN | Press encoder | Top pos / feed enable | Shielded pair |
ESTOP_CHAIN | E-stop loop | Healthy status | Supervise, not control |
K1_CMD / K2_CMD | Safety relay outputs | Power removal | To contactor coils |
ROBOT_PERMIT | Interlock logic | Allow robot to enter | Mutual exclusion |
7) Commissioning & periodic tests
One-time commissioning
- Verify polarity, PE bonding, shield terminations (single-point).
- Check OSSD coherence and EDM blocks reset when K1/K2 are held.
- Confirm encoder angle and feed window; capture screenshots/waveforms.
- Run ISO 13855 calculations; archive as-built drawings and photos.
Quarterly tests
- Test-rod verification (10/30/40 mm as applicable).
- Door/scanner stop distance and timing.
- E-stop Chain → K1/K2 drop times within spec.
Self-test log (CSV copy)
Item,Test,Expected,Actual,Result,Notes
1,OSSD channels,Drop together,,,
2,EDM feedback,Reset inhibited with held K1/K2,,,
3,Encoder feed window,Feed only within window,,,
4,E-stop chain,Category 0/1 verified,,,
5,Robot interlock,Mutual exclusion enforced,,,
6,Safety distance,S = K×T + C recorded,,,
8) Common mistakes & fixes
| Mistake | Symptom | Fix |
|---|---|---|
| Mixing safety and PLC stop paths | Stop not deterministic | Route power removal through safety relay/PLC only |
| No mutual exclusion with robot | Robot near moving press | Hard interlock on press state; zone logic in safety controller |
| OSSD channels share fuse | Hidden single-point failure | Separate protection and harnessing |
| Encoder noise | False window triggers | Shielded cable, proper grounding, debounce/safety-rated inputs |
| Improper ISO 13855 inputs | Distance too small | Use worst-case response time; include relay + contactor drop |
9) FAQ
Can I rely on robot safety alone to stop the press?
No. The press power removal must be independent (safety relay/PLC + K1/K2). Robots add an interlock layer but do not replace the press safety function.
Do I need muting for material feed?
Only if risk assessment shows it’s necessary. Prefer feed windows and mechanical guards first; apply muting with strict conditions and indicators.
What documentation should be filed?
Risk assessment, ISO 13855 sheets, wiring diagrams, I/O list, encoder setup, commissioning logs, and periodic test records.