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 — with safety requirements established by the machine risk assessment. You’ll get wiring patterns, interlock logic, timing references, and audit-ready checklists.
1) Line topology (high-level)
Coil → 3-in-1 Feeder → Infeed Guard → Press (ENC) → Outfeed Guard → Robot Cell → Out Conveyor
[Safety devices]
- Infeed: Risk-assessed protective device; gate interlock on maintenance door (exact function and safety rating validated)
- Press point of operation: Approved safeguard with documented detection and stop function; any blanking/muting requires a separately validated design
- Robot area: Safety laser scanner (zones) or safety fence with interlocked doors
- Global: Risk-assessed E-stop span, validated mode selection and safety logic controlling the required final stopping devices
ENC is ordinary press position feedback unless the complete encoder/input/evaluation function is safety-rated and validated. Before specifying presence-sensing protection, check the clutch and brake: OSHA 1910.217(c)(3)(iii) prohibits this guarding method on full-revolution-clutch presses. This diagram is not approval for any existing press.
2) Safety devices & zones
Light curtains (infeed / POI)
- Both OSSDs to compatible safety inputs; required output feedback through documented safety logic.
- Use documented detection capability, not beam pitch or a generic finger/hand label; verify every reachable access path and protective height.
- Use the applicable ISO 13855:2024 positioning method; retain detection, geometry and full stopping-chain inputs.
Robot cell boundary
- Safety scanner with protective/warning fields and speed/zone switching, or fence + door interlocks.
- Validate reduced-speed and enabling functions in SETUP. Clearing the boundary or re-closing a door must not itself restart motion.
3) Core interlocks (press, feeder, robot)
| Interlock | Condition | Effect | Notes |
|---|---|---|---|
| Press enable | Required safeguards and documented diagnostics satisfied; safe mode valid | Permit the validated clutch/brake/drive safety function | Required safeguard demand/fault removes motion permission |
| Feed window | ENC window active | Allow NC feeder advance | Process collision prevention; not personnel-protection proof |
| Robot interlock | Validated safe press state; hazardous motion prevented | 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 |
Safety-function sequence (non-executable)
CONCEPT ONLY — not executable safety software
1. Evaluate each safeguard through its documented safety input/function block.
2. Remove press-motion permission whenever its required safety function requests a stop.
3. Permit robot entry only after the press safety function confirms hazardous motion
is prevented, not merely because an ordinary TDC bit is high.
4. Inhibit press motion while the robot occupies the protected press zone.
5. Permit normal feeder advance only inside the validated process feed window.
6. Require the documented restart sequence; guard clearing must not start motion.
Standard PLC/HMI copies of these states are diagnostic, not safety authority.Implement through approved safety-function blocks and validate the actual circuit. Ordinary PLC code remains supervisory; the final stopping mechanism depends on the press, feeder and robot design.
4) E-stop loops & power hierarchy
Hierarchy
- Stop category 0: remove power to the relevant actuators for an uncontrolled stop, as required by the validated design; this is not simply a mains-contactor instruction.
- Category 1 (controlled stop): Commanded decel then remove power.
- Define each E-stop's span of control and stopping function so all relevant hazards reach the required safe state.
Loop concept (ASCII)
FUNCTIONAL EXAMPLE — not terminal wiring
E-stop channels → compatible safety logic → required final stopping devices
Prescribed output/stop feedback → documented safety evaluation
Auxiliary status copies → ordinary PLC/robot diagnostics
Mechanical press: validate clutch/brake response and stored energy.
K1/K2 contactors are only an example, not proof that the slide stops.5) Timing: encoder, feed window, muting
- Use the press and die documentation to define the feed window; validate clearance across the complete operating envelope. No generic crank-angle interval applies to every press.
- Light curtain muting/blanking only when material entry is unavoidable and risk assessed.
- Record response times: light curtain, safety relay, final switching devices and machine stop; apply the correct positioning method with worst-case values.
6) Copy-ready I/O map (generic)
| Tag | Source/Device | Purpose | Notes |
|---|---|---|---|
OSSD_A / OSSD_B | Infeed/POI light curtain | Safety channels | Follow sensor/controller supply, test-pulse and wiring requirements |
EDM_FB | K1/K2 NC series | Example required contactor feedback | Use specified mirror contacts and a documented safety evaluation function |
DOOR_OK | Gate interlock switches | Boundary closed | Exact safety interface and lock monitoring where required |
SCANNER_SAFE | Robot area scanner | Zone clear | Protective field |
ENC_TDC / FEED_WIN | Press encoder | Top pos / feed enable | Ordinary position feedback is process control unless safety-rated and validated |
ESTOP_CHAIN | E-stop loop | Healthy status | Supervise, not control |
K1_CMD / K2_CMD | Safety relay outputs | Example final switching command | Only where contactors form part of the validated stopping architecture |
ROBOT_PERMIT | Interlock logic | Safety permission for entry | Mutual exclusion |
7) Commissioning & periodic tests
One-time commissioning
- Verify polarity, protective bonding and shielding against the device and EMC installation instructions; no universal single-point rule.
- Check OSSD coherence and EDM blocks reset under a manufacturer-approved controlled fault test with hazardous motion prevented; never hold or bypass live contactors.
- Confirm encoder angle and feed window; capture screenshots/waveforms.
- Run ISO 13855 calculations; archive as-built drawings and photos.
Scheduled tests
- Detection test using the exact manufacturer's specified test piece and procedure.
- Door/scanner stop distance and timing.
- Complete E-stop function and actual machine stopping performance.
Self-test log (CSV copy)
Item,Test,Expected,Actual,Result,Notes
1,OSSD channels,Manufacturer-specified detection and fault response,,,
2,Required feedback,Approved controlled fault test with hazard prevented,,,
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,Applicable method and complete stop-chain inputs recorded,,,
8) Common mistakes & fixes
| Mistake | Symptom | Fix |
|---|---|---|
| Mixing safety and PLC stop paths | Stop not deterministic | Implement the required stop through validated safety logic and final stopping devices |
| No mutual exclusion with robot | Robot near moving press | Hard interlock on press state; zone logic in safety controller |
| Unverified OSSD interface or test-pulse handling | Nuisance trips or undetected faults | Use manufacturer-approved power, wiring and input modes |
| Encoder noise | False window triggers | Follow EMC design; ordinary debounce does not create a safety-rated position function |
| Improper ISO 13855 inputs | Distance too small | Use worst-case response time; include relay + contactor drop |
9) FAQ
Can robot safety replace the press safety stop?
An ordinary robot interlock cannot replace the press safety function. A supported safety-rated robot or drive function may participate only in a validated architecture. Verify the press clutch/brake and stored-energy behaviour; opening mains contactors alone does not establish a safe slide stop.
When is muting acceptable?
Use muting only when material must pass through the protective field and risk assessment confirms equivalent safety. Apply strict conditions, indicators, and logging.
What periodic tests are required?
Set intervals from the applicable machine requirements, risk assessment and manufacturer instructions. Verify safeguard detection with the prescribed test piece, complete stopping performance, restart prevention and required feedback diagnostics under an approved controlled procedure. Process feed-window checks are separate from validated safety-position functions.
File the risk assessment, stopping-distance assessment, approved schematic and I/O list, feed-window setup, commissioning results and periodic test records.