Risk assessment steps, safety functions and cobot collaboration types.
The safety of a robot cell is the most critical part of a project in legal, ethical and commercial terms. Safety design is not hardware added afterwards but the first step of cell design. Here is the basic framework.
Which standards apply?
- ISO 10218-1: Safety requirements of the industrial robot itself (robot manufacturer)
- ISO 10218-2: Safety requirements for robot systems and cell integration (integrator)
- ISO/TS 15066: Force and pressure limits for collaborative robots
- ISO 13849-1: Performance level (PL) of safety control systems
- 2006/42/EC Machinery Directive: The legal framework for CE marking
How is a risk assessment done?
- Determining limits: The intended use of the cell, working area and operator intervention points are defined.
- Hazard identification: All hazards are listed, such as crushing, impact, trapping, weld flash, noise and part ejection.
- Risk evaluation: For each hazard, severity, exposure frequency and possibility of avoidance are scored.
- Risk reduction: First by design (rounded edges, speed limit), then by guarding (fence, light curtain), and last by instruction and training.
- Verification: The real performance of safety functions is measured (stopping distance, response time).
Safety functions
- Safe stop (STO / SS1 / SS2)
- Safely limited speed and area limiting
- Speed reduction and stop zones with an area scanner
- Two-hand start, interlocked door switch
Four types of collaboration in cobots
The four types defined in ISO 10218: safety-rated monitored stop, hand guiding, speed and separation monitoring, power and force limiting. If the application has a hazardous end (sharp tool, welding torch), protection is needed even with a cobot; not only the robot itself but also the workpiece and end tool enter the risk assessment.
Common mistakes
- Performing the risk assessment after design is finished; the cost of changes rises sharply
- Not considering maintenance and setup situations in which the operator must enter the cell (mode 2 – T1 speed)
- Not including the end tool and sharp edges of the workpiece in the cobot risk assessment
- Not revalidating after changing the safety system through software
Commissioning checklist
Emergency stop tests, door interlock tests, area scanner zone verification, stopping distance measurement and operator training are recorded. Eksen delivers this verification report with the CE file for all its cells.