AGV/AMR: safety scanner vs industrial LiDAR
Aisles, obstacle avoidance & speed monitoring. This engineer-focused guide clarifies when to use a safety laser scanner (PL-rated stop fields and Speed & Separation Monitoring) versus an industrial LiDAR (navigation/SLAM & obstacle avoidance). It includes design rules, stopping-distance math inputs, and acceptance logs suited for audits.
Non-negotiable: Navigation LiDARs are not safety-rated. The certified stop chain is: safety input (scanner/E-stop/bumpers) → safety controller/relay → force-guided contactors K1/K2. PLC navigation only supervises and commands speed; it does not perform the safety stop.
1) Clear roles: safety vs navigation
Safety laser scanner (certified)
- Creates protective fields (hard stop) and warning fields (slowdown/SSM).
- Dual OSSD outputs; parameter locks; tamper-evident records.
- Use at perimeter of the vehicle or fixed areas (dock, transfer station).
Industrial LiDAR (navigation/SLAM)
- Builds maps, localizes the vehicle, plans paths, and avoids obstacles.
- Outputs to the motion controller (velocity/turn rate); not a safety function.
- Great for crowded aisles, rack reflections, mixed pallets — paired with safety sensors.
2) Quick decision table
| Question | Prefer safety scanner | Prefer industrial LiDAR |
|---|---|---|
| Need certified stop on human entry? | Yes — use protective field OSSD | No — LiDAR for navigation only |
| Speed & Separation Monitoring (SSM)? | Yes — warning→stop fields | Handled by nav stack (non-safety) |
| Global mapping & localization? | Not applicable | Yes — SLAM/odometry fusion |
| Budget & complexity | Sensor cost higher; simpler integration | Sensor cost lower; requires nav stack |
| Reflective floor, tight turns | Use angled mounting, multiple fields | Use multi-echo/filters; fuse with camera |
3) Proven zone patterns for vehicles
A. Forward travel
- Front scanner: Protective short field; Warning long field.
- Rear/side scanners mirrored for cornering.
- Switch sets on speed bands and steering angle.
B. Station docking
- Narrow protective field to block crowding during docking.
- Interlock with station light curtains/doors via EDM.
- Disable auto-resume until edges clear + reset.
C. Reverse or tug mode
- Rear scanner becomes primary; trailer swing area covered.
- Wide side warning fields; crawl-speed cap.
- Fork/arm attachments add separate field sets.
4) Stopping distance worksheet (copy)
Vehicle mass m (kg) = ?
Max speed v_max (m/s) = ?
System response time T (s) = sensor + controller + brake delay
Deceleration a_safe (m/s²) = measured under full load
Safety margin M (m) = tire slip, slope, floor
Braking distance: D_brake = v^2 / (2 × a_safe)
Total stopping distance: D_total = v × T + D_brake + M
For SSM: choose warning field so that at v_max the vehicle can slow to v_safe
or stop before entering the protective field boundary.Record measured delays (scope/meter logs). Do not rely on catalog values alone.
5) Wiring baseline (scanner + controller)
// Safety scanner
OSSD1 ─────► IN_CH_A (Safety controller)
OSSD2 ─────► IN_CH_B (Safety controller)
Mode Sel ──► Field set inputs (Slow / Normal / Dock)
EDM FB ───► From K1/K2 NC in series
// Power removal
Out 13-14 / 23-24 ─► K1/K2 coils (drive enable off)
// Navigation LiDAR (non-safety)
Ethernet/Serial ─► Nav computer (SLAM/obstacle avoidance)
Nav outputs ────► Motion controller (velocity/turn rate) // supervised onlyReplace with your certified function blocks. PLC/nav code is supervisory, not safety-rated.
6) Commissioning & periodic tests
Commissioning checklist
- Verify OSSD dual-channel coherence; EDM blocks reset with held K1/K2.
- Measure response time T; log field screenshots and parameter seals.
- Validate mode switching (speed, steer, reverse, dock).
- Navigation: confirm obstacle avoidance yields bounded jerk and no dead-locks.
Quarterly tests
- Approach tests at each speed band: warning→stop distances met.
- Blind-spot checks (pallet corners, low obstacles).
- Re-measure braking distance under max payload and worst floor.
Test log (CSV copy)
Item,Test,Expected,Actual,Result,Notes
1,OSSD coherence,Channels drop together,,,
2,EDM welded-contact block,Reset inhibited when K1/K2 held,,,
3,Mode switching,Correct fields vs speed/steer/reverse,,,
4,SSM distance,Slow/stop within D_total,,,
5,Nav avoidance,No dead-lock; bounded jerk,,,
7) Common mistakes & fast fixes
| Mistake | Symptom | Fix |
|---|---|---|
| Using nav LiDAR as the safety device | No certified stop; unknown latency | Install safety scanner; keep LiDAR for SLAM only |
| Single-channel OSSD | Hidden single fault | Always dual OSSD with independent harness/fusing |
| No parameter sealing/logs | Audit failure; unsafe changes | Seal configs; export and archive parameter sets |
| Underestimating stopping distance | Overrun into hazard | Measure T and a_safe loaded; add margin M for floors/slopes |