Deploying a collaborative robot without a documented risk assessment is not just a safety risk — it is a regulatory violation in most jurisdictions. Under ISO 10218-2 and ISO/TS 15066, the system integrator (or end user who performs their own integration) is legally responsible for conducting and documenting a risk assessment before a cobot cell goes live.
This guide walks through the complete risk assessment process step by step — from hazard identification through biomechanical limit verification — with the documentation templates and checklists used in compliant deployments.
Quick Answer: A cobot risk assessment follows ISO 12100 (general machinery risk assessment methodology), applies ISO 10218-2 (robot integration safety), and uses ISO/TS 15066 to verify that contact forces stay within human pain threshold limits. The output is a documented risk file that must be retained for the life of the installation.
Why Cobots Still Need Risk Assessments
A common misconception: "It's a cobot — it's inherently safe." This is wrong in two ways:
- No robot is inherently safe for all applications — A cobot with a sharp end-of-arm tool (drill bit, knife, needle) can cause serious injury regardless of its built-in force limits
- ISO/TS 15066 defines limits, not guarantees — The standard provides biomechanical force thresholds for different body regions. Meeting those thresholds requires application-specific verification — not just buying a cobot with built-in safety features
Regulatory bodies in the EU (Machinery Directive 2006/42/EC, being replaced by Machinery Regulation 2023/1230), North America (ANSI/RIA R15.06), and increasingly in China (GB/T 38244) all require documented risk assessment for robotic installations.
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The Risk Assessment Framework: Three Standards
ISO 12100 — The Foundation
ISO 12100 (Safety of Machinery — General Principles for Design) defines the Risk Assessment and Risk Reduction iterative process used for all machinery, including robots:
- Determine the limits of the machinery (intended use, foreseeable misuse, persons at risk)
- Identify hazards (systematic hazard identification across all machine states)
- Estimate risk (severity × probability × avoidability)
- Evaluate risk (acceptable or requires reduction?)
- Reduce risk (inherently safe design → safeguarding → information for use)
- Repeat until residual risks are acceptable
ISO 10218-2 — Robot Integration Requirements
ISO 10218-2 (Robots and Robotic Devices — Safety of Industrial Robots — Part 2: Robot Systems and Integration) covers the safety requirements for robot cells, including:
- Safeguarding requirements for different robot modes
- Speed and force limits for collaborative operation
- Requirements for emergency stop, protective stop, and speed reduction
- Documentation requirements for the technical file
ISO/TS 15066 — Collaborative Operation Specifics
ISO/TS 15066 (Robots and Robotic Devices — Collaborative Robots) is the key standard for cobot-specific safety. Its most important contribution: Annex A biomechanical force and pressure limits for 29 body regions.
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Step 1: Define the Application and Limits
Before identifying hazards, document:
1.1 Intended Use Statement
- What task does the robot perform?
- What product/part does it handle?
- What is the production environment (temperature, lighting, other workers)?
- Who operates it? (trained operators, maintenance technicians, passersby)
1.2 Robot System Limits
| Parameter | Value to Document |
|---|---|
| Robot model and payload | e.g., UR10e, 10 kg max payload |
| Actual working payload | e.g., 3.2 kg (part + gripper) |
| Maximum speed in collaborative mode | e.g., 250 mm/s (application limit) |
| Maximum TCP force limit | e.g., 150 N (configured in safety settings) |
| Collaborative workspace boundary | e.g., 800 mm radius from robot base |
| End-of-arm tooling | e.g., parallel gripper, no sharp edges |
1.3 Foreseeable Misuse
Document predictable ways the robot could be misused:
- Operator reaches into workspace to grab a dropped part
- Maintenance technician works near robot while it's in reduced-speed mode
- Robot carries an unapproved, heavier part that affects stopping distance
- Safety scanner is defeated to increase production speed
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Step 2: Systematic Hazard Identification
Work through each machine state and identify all hazards:
Machine States to Analyze:
- Normal production operation
- Manual loading / unloading
- Changeover / product change
- Cleaning and maintenance
- Abnormal operation (jam clearing, error recovery)
- Installation and commissioning
- Decommissioning
Hazard Categories for Cobots (ISO 10218-2 Annex B):
| Category | Examples |
|---|---|
| Mechanical — contact | Crushing, striking, pinching from robot arm motion |
| Mechanical — EOAT | Cutting, piercing, entanglement from end-of-arm tooling |
| Mechanical — workpiece | Dropped parts, ejected workpieces |
| Ergonomic | Awkward posture at HMI, repetitive loading motions |
| Electrical | Control panel access, grounding failures |
| Thermal | Hot parts, welding sparks (application-specific) |
| Noise/vibration | Prolonged exposure (application-specific) |
| Environmental | Slipping hazard from dropped parts or lubricants |
Use a structured Hazard Log:
```
Hazard ID | Machine State | Hazard | Persons at Risk | Initial Risk Level | Risk Reduction Measure | Residual Risk
H-001 | Production | Robot arm strikes operator reaching into workspace | Operator | High | PFL + safety-rated reduced speed | Low
H-002 | Loading | Gripper closes on operator's hand | Operator | High | Presence sensing + reduced force | Low
H-003 | Maintenance | Robot moves during manual mode | Maintenance tech | High | Speed reduced to 250 mm/s, tech holds dead man switch | Low
```
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Step 3: Collaborative Operation Mode Selection
ISO/TS 15066 defines four collaborative operation modes. Identify which mode(s) your application uses:
Mode 1: Safety-Rated Monitored Stop (SMS)
Robot stops when person enters the workspace. Resumes when person leaves. No contact between robot and person during motion.
When to use: Loading/unloading stations where the operator and robot never move simultaneously.
Mode 2: Hand Guiding (HG)
Operator physically guides the robot. Requires a hand-guiding device on the TCP with force sensing. Safety-rated speed monitoring limits robot speed.
When to use: Teach pendant replacement for complex paths; assembly assistance.
Mode 3: Speed and Separation Monitoring (SSM)
Robot continuously reduces speed as operator approaches. Distance measured by safety-rated sensors (area scanners, 3D cameras). When separation = minimum, robot stops.
When to use: Shared workspaces where human and robot both work simultaneously in overlapping areas, without contact.
Mode 4: Power and Force Limiting (PFL)
Robot detects contact and limits force/power to stay within ISO/TS 15066 biomechanical limits. No additional guarding required if limits are verified.
When to use: True collaboration — robot and human work in physical contact or near-contact simultaneously. Most commonly deployed mode for cobots.
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Step 4: Biomechanical Limit Verification (ISO/TS 15066 Annex A)
This is the most critical and most frequently skipped step.
ISO/TS 15066 Annex A provides force and pressure limits for 29 body regions based on human pain threshold research. Contact above these limits causes pain; contact below is considered acceptable for transient contact.
Key Limits (Selected Body Regions):
| Body Region | Quasi-static Force Limit | Transient Force Limit | Pressure Limit |
|---|---|---|---|
| Skull/forehead | 130 N | 130 N | 110 N/cm² |
| Face | 65 N | 65 N | 110 N/cm² |
| Neck (front) | 145 N | 145 N | 50 N/cm² |
| Shoulder | 160 N | 210 N | 160 N/cm² |
| Upper arm | 160 N | 210 N | 160 N/cm² |
| Lower arm | 160 N | 240 N | 180 N/cm² |
| **Hand (palm)** | **140 N** | **180 N** | **180 N/cm²** |
| **Fingers** | **140 N** | **180 N** | **300 N/cm²** |
| Chest | 120 N | 140 N | 120 N/cm² |
| Abdomen | 110 N | 110 N | 100 N/cm² |
| Thigh | 220 N | 250 N | 250 N/cm² |
| Lower leg | 220 N | 250 N | 250 N/cm² |
| Foot | 130 N | 130 N | 220 N/cm² |
*Quasi-static = sustained contact; Transient = brief collision contact.*
How to Verify Compliance
Method 1: Force measurement (recommended) — Use a calibrated biomechanical measurement device (e.g., Pilz PMC, ATI force/torque sensor + measurement tool, Fraunhofer measurement kit) to physically measure peak force and pressure during contact with the actual tool at the configured speed and force limits.
Method 2: Analytical calculation — Calculate effective mass and speed, then use the collision force model in ISO/TS 15066. Acceptable for initial estimation but physical measurement is required before final sign-off.
Method 3: Manufacturer certification — Some robot OEMs (UR, Fanuc CRX, Techman) provide pre-certified configurations for specific payloads and speeds. Verify that your specific EOAT and payload are within the certified configuration.
Critical: EOAT Matters as Much as Robot Force Limits
A cobot set to 150 N force limit with a pointed gripper tip (1 cm² contact area) delivers 150 N/cm² pressure — potentially above pain threshold for sensitive body regions. The force limit alone does not determine compliance — contact geometry matters.
Design guidelines for compliant EOAT:
- Minimum contact area: typically 4–10 cm² for hand contact zones
- No sharp edges, protrusions, or exposed fasteners in contact zones
- Consider padding for rounded surfaces in high-risk contact zones
- Document EOAT geometry in the risk assessment technical file
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Step 5: Risk Evaluation and Reduction
For each hazard in the Hazard Log, apply the risk reduction hierarchy (ISO 12100 Clause 6):
- Inherently safe design — Can the hazard be eliminated by design? (remove sharp features, change robot path to avoid high-contact-risk zones)
- Safeguarding — Technical safeguards (PFL configuration, SSM scanners, safety stops)
- Information for use — Operator training, warning labels, procedures
Document the residual risk for each hazard after reduction measures. Residual risk must be acceptable — either by comparing to ISO/TS 15066 limits (for PFL) or by demonstrating equivalent protection (for other modes).
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Step 6: Documentation and Technical File
For CE marking (EU) or equivalent certification, the technical file must include:
Mandatory Documentation Checklist
- [ ] Risk assessment report (this document, following ISO 12100 structure)
- [ ] Hazard log with all hazards, risk levels, reduction measures, residual risks
- [ ] Biomechanical force measurement report (ISO/TS 15066 Annex A verification)
- [ ] Safety function documentation (PFL settings, SSM zone geometry, stop time/distance analysis)
- [ ] Robot safety parameter record (speed limits, force limits, workspace limits as configured)
- [ ] EOAT design specification and contact geometry analysis
- [ ] Operator training records
- [ ] Maintenance and inspection procedures
- [ ] Declaration of Conformity (for EU CE marking)
- [ ] Electrical schematic with safety circuit documentation
- [ ] Emergency stop function test records
Stop Time and Distance Analysis
For SSM (Speed and Separation Monitoring), you must calculate the minimum separation distance using:
S = (T_s + T_r) × v_h + C
Where:
- S = minimum separation distance (mm)
- T_s = maximum time for machine to reach safety-related stop (measured)
- T_r = response time of safety sensor system (from manufacturer)
- v_h = approach speed of human (ISO/TS 15066 uses 1,600 mm/s for hand/arm)
- C = intrusion distance (from ISO 13855)
This calculation must be documented for each SSM configuration.
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Common Risk Assessment Failures
| Failure Mode | Consequence |
|---|---|
| Risk assessment done after installation | Non-compliant; may require removal/rework of guarding |
| EOAT not included in force measurement | Force limits met but pressure limits exceeded |
| Maintenance mode not assessed | Maintenance technicians working in reduced-speed mode without documented protection |
| Operator training not documented | Cannot demonstrate personnel protection measures were implemented |
| No residual risk statement | Incomplete technical file; CE marking not valid |
| Biomechanical limits not physically measured | Analytical calculation insufficient for final certification |
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Frequently Asked Questions
Is a risk assessment required for every cobot installation?
Yes. ISO 10218-2 requires a risk assessment for every robot system installation, regardless of whether the robot is collaborative or industrial. The risk assessment methodology and depth varies — a simple machine tending cell may have a simpler assessment than a complex collaborative assembly cell — but it cannot be skipped.
Who is responsible for the cobot risk assessment?
The system integrator, or the end user if they perform their own integration. Under the EU Machinery Regulation, the party that places the final system on the market bears responsibility for the CE declaration and underlying risk assessment.
Does buying an ISO-certified cobot mean no risk assessment is needed?
No. The robot manufacturer certifies the robot product (ISO 10218-1). The system integrator must conduct a separate application-level risk assessment for the robot cell (ISO 10218-2). The robot's safety certifications are inputs to the cell-level assessment, not substitutes for it.
How long does a cobot risk assessment take?
For a simple single-cobot cell: 2–5 days (hazard identification + documentation + biomechanical measurement). For complex cells with SSM and multiple collaborative modes: 1–3 weeks. Budget $5,000–$15,000 for external safety consultant support.
What is the difference between ISO 10218 and ISO/TS 15066?
ISO 10218 (Parts 1 and 2) is a full International Standard covering all industrial robots, including safety requirements for collaborative operation modes. ISO/TS 15066 is a Technical Specification that specifically addresses collaborative robots, providing the biomechanical force/pressure limits and application guidance for Power & Force Limiting (PFL) operations. Both documents are used together for cobot risk assessments.
Can I do the risk assessment myself, or do I need a certified consultant?
You can perform your own risk assessment — there is no legal requirement to use a certified external consultant. However, the assessment must be competent and thorough. If you lack experience, using a TÜV, SGS, or PILZ safety consultant for the first assessment is advisable, then build internal capability from their methodology.
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