Robot Safety Standards and Collaborative Modes

Industrial robots used to work behind fences. Collaborative robots share space with people, so safety standards, chiefly ISO 10218 and the technical specification ISO/TS 15066, define four ways a robot may work near people. Each mode trades productivity against how close a person may come and how hard any contact can be.

Collaborative mode Person's walking speed Robot's full speed Robot reaction plus stopping time

Four collaborative modes

Safety-rated monitored stop: the robot stops and holds still, monitored by a safety-rated system, whenever a person enters the shared space. Hand guiding: a person moves the robot directly with an enabling device. Speed and separation monitoring: the robot slows as people approach and stops before contact. Power and force limiting: contact may happen, but the robot is designed and limited so the forces stay below thresholds set for different body regions.

Protective separation distance

Speed and separation monitoring keeps the person beyond a protective distance that covers how far both can move before the robot has fully stopped. A simplified form, with person speed $v_h$, robot speed $v_r$, reaction plus stopping time $T$, and a margin $C$ for sensing uncertainty and intrusion, is

$$S_p \approx v_h\,T + v_r\,T + C$$

The standard's full expression separates reaction and stopping times and the robot's braking. Values on this page are illustrative.

What to notice

A faster walker or a slower-stopping robot pushes the protective distance out, so the robot starts slowing earlier. In monitored-stop mode it simply halts, which is safe but stops production. Power and force limiting lets the robot keep moving near people only because it is slow and light enough that contact stays below the limits, which is why collaborative arms are slower than caged ones. Real deployments start with a risk assessment that decides which modes are acceptable.