Robot Safety Standards & RFP Guide

5-2. ISO 3691-4 Compliance & Safety Engineering Guide

1. AGV/AMR Safety Device Performance & ISO 3691-4 Standards

ISO 3691-4:2020 (Safety requirements for driverless industrial trucks and their systems) serves as the global de facto safety engineering standard for AGVs and AMRs[cite: 20]. Unlike legacy guidelines, it strictly regulates "functional safety" across the entire integrated system rather than evaluating sensors in isolation[cite: 20].

1.1 Functional Safety Requirements (PL / SIL) Under ISO 3691-4

ISO 3691-4 mandates that Safety-Related Control Systems (SCS) in autonomous mobile robots achieve Performance Levels (PL) governed by ISO 13849-1[cite: 20]:

• Speed, Steering, and Emergency Stop Control: Mandatory functional safety reliability of PL d or higher (Category 3 or higher)[cite: 20].
• Redundancy Mandates: Dual-channel control architecture is required so that a single component failure in sensors (LiDAR) or brake circuits will not cause a loss of safety functions[cite: 20].

1.2 Primary Safety Devices & Technical Performance Criteria

Multi-layered protection systems combine safety devices based on robot velocity, inertial mass, and operational zones[cite: 20]:

Safety Device	Primary Function & Installation Criteria	ISO 3691-4 / Standard Performance Requirements
2D Safety Laser Scanner (LiDAR)	Primary obstacle and personnel detection (Primary Safety Sensor)[cite: 20]	• Mandatory safety certification (IEC 61496 Type 3 / PL d)[cite: 20]. • Dynamic adaptive field switching for Warning and Stop zones based on speed[cite: 20]. • Reliable detection down to low floor clearance levels (150mm–200mm max)[cite: 20].
Safety Contact Bumper	LiDAR blind spot coverage & mechanical emergency stop on impact[cite: 20]	• Positive mechanical switches bringing the vehicle to an immediate stop (PL d equivalent)[cite: 20]. • Cushion compression deformation exceeding vehicle braking distance[cite: 20].
3D Cameras & Volumetric Sensors	Detecting elevated, hanging, or diagonal obstacles (e.g., overhangs, forklift tines)[cite: 20]	• Detects overhead risks or floating loads undetectable by 2D LiDAR[cite: 20]. • Ambient light immunity against sunlight or lighting reflections[cite: 20].
Emergency Stop Button (E-STOP)	Manual full-stop override[cite: 20]	• Red palm button on yellow background complying with ISO 13850[cite: 20]. • Accessible from all vehicle directions, executing immediate Category 0 or 1 power shutoff[cite: 20].

1.3 Detection Zone (Protection Field) Design Rules

ISO 3691-4 requires aligning sensor detection zones directly with total stopping distances[cite: 20]:

• Speed-Adaptive Zone Switching: Automatically adjusts detection field length and shape during straight travel, cornering, and acceleration/deceleration[cite: 20].
• Blind Spot Mitigation: If turning or reversing maneuvers leave travel directions unmonitored, speeds must be reduced significantly or protected by mechanical safety bumpers[cite: 20].

1.4 Operational Modes & Human Coexistence Restrictions

• Low-Speed Coexistence Limits: In shared human-robot work zones, vehicle speed is strictly capped at ≤0.3 m/s (approx. 1.08 km/h) if detection fields are reduced[cite: 20].
• Prohibition of Automatic Auto-Restart: Following an emergency stop or safety sensor trip, robots must not automatically restart when obstacles clear; a manual reset or deliberate restart sequence is required[cite: 20].

2. ISO 3691-4 Verification & Compliance Checkpoints

When procuring AGVs or AMRs, verifying third-party certification and site-level integration is far more critical than relying on manufacturer catalog claims alone[cite: 20].

2.1 Documentation & Compliance Audit

Verify whether compliance relies on manufacturer self-declaration or certified third-party testing[cite: 20]:

• Third-Party Certification Certificates (TÜV, SGS, UL, etc.):[cite: 20]
  • For overseas equipment, verify that the CE Declaration of Conformity (DoC) cites ISO 3691-4:2020[cite: 20].
  • Request formal Certificates of Conformity issued by accredited testing bodies[cite: 20].
• Functional Safety (PL d / SIL 2) Reports:[cite: 20]
  • Review ISO 13849-1 SISTEMA calculation reports confirming dual-channel safety circuit architectures[cite: 20].
• Risk Assessment (RA) Documentation:[cite: 20]
  • Confirm manufacturer risk assessment documentation detailing hazard identification and risk reduction is provided[cite: 20].

2.2 Hardware & Physical Safety Evaluation

Evaluate physical hardware compliance against ISO 3691-4 requirements[cite: 20]:

Evaluation Item	ISO 3691-4 Audit Checkpoint
Safety LiDAR Selection	Verify 2D LiDAR units are certified safety-rated sensors (IEC 61496 Type 3 / PL d) rather than standard industrial measurement LiDAR[cite: 20].
E-STOP Wiring Architecture	Confirm E-STOP activation physically cuts main motor power (Category 0/1 stop) without relying on software[cite: 20].
Overhead & Volumetric Detection	Verify 3D sensors detect hanging loads or overhead obstacles in blind zones[cite: 20].
Full-Load Stopping Distance	Confirm full-speed emergency stopping distances under max payload fall within active LiDAR protection zones[cite: 20].
Manual Safety Reset Sequence	Ensure clearing an obstacle requires manual reset action before vehicle motion resumes[cite: 20].

2.3 System Integration (SI) & Site Environment Compliance

ISO 3691-4 governs the entire operating environment, not just standalone vehicles. Improper site mapping or narrow clearances invalidate compliance[cite: 20].

• Operating Zone Classification:[cite: 20]
  • Verify Clear Zones (fenced), Coexistence Zones, and Working Zones are correctly designated in fleet software[cite: 20].
• Clearance Safety Distances & Pinch Point Mitigation:[cite: 20]
  • Ensure ≥0.5m pedestrian clearance is maintained along travel lanes; narrow zones must enforce automatic creep speeds[cite: 20].
• Facility Interlocks:[cite: 20]
  • Confirm fail-safe stop sequences execute during communication loss with auto doors, fire shutters, or VMCs[cite: 20].

3. RFP & Procurement Specification Templates

Procurement specifications (RFP) should state concrete, verifiable ISO 3691-4 functional safety requirements[cite: 20]:

3.1 Sample RFP Clauses for AGV/AMR Safety Requirements

[Clause Title: Autonomous Mobile Robot (AGV/AMR) System Safety Compliance][cite: 20]

1. Basic Safety Standard Conformance:[cite: 20]
   • The system (vehicles, fleet management, site integration) shall fully comply with ISO 3691-4:2020[cite: 20].
   • Safety-critical control circuits (speed, steering, E-STOP) shall meet or exceed ISO 13849-1 Performance Level d (PL d / Category 3)[cite: 20].
   • Bidders shall submit third-party Certificates of Conformity (TÜV, SGS, UL) or formal DoC technical files upon delivery[cite: 20].
2. Safety Devices & Protection Functions:[cite: 20]
   • Primary Sensors: Vehicles shall feature IEC 61496 Type 3 / PL d certified 2D safety LiDAR with dynamic speed-adaptive field switching[cite: 20].
   • 3D Volumetric Detection: 3D cameras or ultrasonic sensors shall complement 2D LiDAR to detect overhangs and floating obstacles[cite: 20].
   • E-STOP Circuitry: ISO 13850 compliant emergency stop buttons shall directly sever motor power upon activation[cite: 20].
   • Manual Safety Reset: Clearing an emergency stop condition shall require manual reset before motion resumes[cite: 20].
3. Site System Integration & Engineering Safety:[cite: 20]
   • System integrators shall configure ISO 3691-4 operating zones (Clear, Coexistence, Working) within site maps[cite: 20].
   • Travel lanes with <0.5m pedestrian clearance shall enforce automatic speed reduction to ≤0.3 m/s[cite: 20].

3.2 Vendor Evaluation & RFP Checklist

Category	Evaluation Checklist Item	Required Document / Deliverable
Documentation	Third-Party Certification	Copy of ISO 3691-4 Certificate of Conformity or CE DoC file[cite: 20].
	Functional Safety Calculations	ISO 13849-1 SISTEMA calculation reports confirming PL d architecture[cite: 20].
	Site Risk Assessment Report	Site-specific Risk Assessment (RA) report covering vehicles and site layout[cite: 20].
Hardware	Safety LiDAR Certification	Verification that LiDAR models are safety-rated (Type 3 / PL d)[cite: 20].
	Full-Speed Stopping Distance	Test data confirming full-load stopping distance falls within LiDAR protection zone[cite: 20].
SI & Operations	Aisle Clearances & Speed Limits	Automated speed reduction program verified for aisles with <0.5m clearance[cite: 20].